Highly absorbent composite compositions, absorbent sheets provided with the compositions, and process for producing the same

ABSTRACT

A composite structure mainly composed of hydratable fine fibers in the form of microfibril and a water swellable solid body, the fine fibers being obtained from cellulose or a derivative thereof, and at least part of the surface of the solid body is covered with the fine fibers. The absorbent composite can be formed in various form of, for example, particle, pellet, sheet and the like, especially of a sheet type with a supporting sheet of a non-woven fabric. The present invention further provides a method of making the composite structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new type absorbent composite whereina water swellable solid body, particularly consisting of particles ofvarious sizes and shapes from powder to pellets is improved infunctioning and handling characteristics. More particularly, the presentinvention relates to a highly absorbent composite composed of orcontaining an absorbent polymer as a water swellable solid body andhaving a shape entirely different from conventional absorbent materialsand a capability of stably absorbing a liquid of much higher quantitythan its own volume and to a highly absorbent composite mainly composedof the composite.

The highly absorbent composite of the present invention can widely beused in diapers for babies and adults, feminine hygiene products,products for handling liquid and solid wastes of animals, and medicalblood absorbent products just like conventional highly absorbentproducts and thus is particularly useful as a super thin pulplessabsorbent making the best use of the capabilities of a so-calledabsorbent polymer. In addition, the absorbent composite can be used fora cold insulator, water holding material, an anti-dewing material,covering material of submarine cables, material for preventing waterrelated accidents.

In addition, the present invention relates to methods and apparatusesfor making the absorbent composite and the composite mainly composed ofthe absorbent composite.

Moreover, the present invention relates to an absorbent sheet whichprovides also the leakage resistance of a conventional backsheet whenthe absorbent composite is used in absorbent products in combinationwith various sheet substrates, to an absorbent sheet which provides alsothe acquisition capability of a conventional topsheet when the absorbentcomposite is used in absorbent products in combination with varioussheet substrates, and to an absorbent sheet which can be used aloneproviding also the capabilities of conventional backsheet and topsheet.

2. Prior Art

A main absorbent component used in an absorbent product, which absorbswater and liquid exudates, is composed of a combination of fluff typewood pulp and so-called super absorbent polymer (hereinafter referred toas the “SAP”). However, in recent years, in order to improve thedistribution efficiency of absorbent products, to reduce the inventoryand display space thereof, and to save natural resources, social needsfor reducing the dimensions of otherwise relatively bulky absorbentproducts are becoming strong.

A means for making an absorbent product more compact and thinner, in acombination of SAP and pulp, would be to increase the content of SAPthat has a higher absorbency than that of pulp by 2 to 10 times andaccordingly decrease the content of pulp. Eventually, if the content ofthe SAP is made 100 percent, the thinnest and most compact absorbentproduct would be able to be obtained.

However, as the content of the SAP increases, when it absorbs water,so-called “gel blocking phenomenon” due to the characteristic of SAPoccurs. Thus, the absorbent product does not work as designed. At thepresent time, it is said that the ratio of the contents of the SAP andpulp is at most 1 to 1. A structure in which the ratio of the contentsof the SAP to pulp is 2 or higher to 1, or so-called pulpless in whichthe content of the SAP is nearly 100 percent is very difficult toachieve at the present time. According to the conventional conceptsgenerally applied in the field of absorbent products, the term“pulpless” means that the ratio of the contents of pulp to the SAP isapproximately 1 or lower.

So far, various attempts for the pulpless structure have been made. Afiber type or web type SAP is made by directly spinning into acrylicacid type fiber or partially hydrolyzing acrylic acid type fiber.Another method is to make a web type absorbent polymer by impregnating aweb with a monomer such as acrylic monomer and then polymerizing themonomer applying ultraviolet ray or electron beam. Still other method isto make an absorbent polymer sheet by carboxymethylating a non-wovenfabric of cellulose or the like and then partially cross-linking thecarboxymethyl cellulose.

However, so far, no successfully commercialized examples have beenreported because of high costs of raw materials and high capitalinvestments involved.

Liquid exudates discharged from living bodies are very different fromeach other depending upon their environmental and living conditions, andthe frequency of discharging is not constant among them. Therefore,absorbent sheets used in many kinds of absorbent products need,responding to varied environs, to exhibit stably the capability ofabsorbing quickly and frequently.

As described above, a conventional two component (pulp and the SAP)absorbent is capable of meeting the need of frequently absorbing to someextent by taking advantage of the temporary retaining by pulp of liquidsand the stably retaining by the SAP of liquids. However, an absorbentproduct in which the content of the SAP is made high or the SAP alone isused in order to secure high absorbency has a serious drawback; upon aliquid being discharged at first the SAP starts to absorb it all at onceand thus an initial absorbing is very speedy but as the discharging isrepeated, the absorbing speed drastically decreases.

SUMMARY OF THE INVENTION

A first embodiment of the present invention provides a highly absorbentcomposite comprising hydratable fine fibers in the form of microfibrilobtained from cellulose or an derivative thereof, and water swellablesolid particles, at least part of the surfaces of said water swellablesolid particles being covered with said fine fibers in the form ofmicrofibril.

Said hydratable fine fibers in the form of microfibril obtained fromcellulose or an derivative thereof useful in the present invention willbe hereinafter referred to as the “HFFM”.

The absorbent composite can be formed in a three dimensional structuresuch as powder type, particle type, pellet type, sheet type, and anyother type, and also in a sheet type with a supporting sheet of anon-woven fabric or the like as the base.

The present invention further provides a method of making the absorbentcomposite. The method comprises the steps of dispersing a waterswellable solid body and the HFFM, in a dispersion medium comprising amixture of an organic solvent and water, the organic solvent beingcapable of controlling the swelling of the water swellable solid bodyand dispersing the HFFM and thus being miscible with water, ofseparating the water swellable solid body and the HFFM from theresultant dispersion liquid from the dispersion medium, and of removingthe liquid component and of drying them.

The absorbent composite of the present invention is basically acomposite of a water swellable solid body and the HFFM covering thesolid body. Examples of a water swellable solid body are various kindsof polysaccharides, flocculents, super water swellable absorbent polymer(the SAP) particles and the like. Among them, a drawback of the SAP,which is that the SAP is not easy to handle and store because of itshigh water absorbency, can be solved by covering it with the HFFMaccording to the present invention. In addition, in a structure in whichthe SAP particles are bonded together with the HFFM, the SAP particlesare each held in position by the HFFM and an appropriate spacesurrounding each particle is secured. Thus, an extremely thin absorbentsheet is obtained.

A second embodiment of the present invention provides an absorbentsheet, wherein a supporting sheet and an absorbent layer provided on atleast either surface of the supporting sheet are provided and whereinthe absorbent layer has the HFFM, the SAP particles, and a short-cutstaple fiber component having longer fiber length than the averageparticle diameter of the SAP particles and has an improved dimensionalstability when wet swollen.

In the present invention, the short-cut staple fiber component havinglonger fiber length a than the average diameter of the SAP particlesconnects the SAP particles with each other and at the same time providesa network structure which covers in network the top surface of a layerformed by the SAP particles and thus serves to prevent the SAP particlesas wet swollen from going away.

The present invention further provides a method of making the absorbentsheet. The method comprises the steps of preparing a three-componentdispersion slurry by adding and dispersing a short-cut staple fibercomponent and the SAP particles in a dispersion liquid wherein the HFFMis dispersed in a dispersion medium, of forming a layer of the slurry byspreading the three-component dispersion slurry onto a supporting sheet,of removing the dispersion medium from the slurry layer, and then ofdrying.

The absorbent sheet of this embodiment of the present invention consistsof four components the SAP particles, the HFFM, a short-cut staple fibercomponent, and a substrate fabric supporting them. The SAP particles area basic component giving a water absorbing capability. The SAP isavailable in various forms such as film and non-woven fabric besides theabove described particles.

The HFFM prevents the SAP from settling as the dispersion stabilizer andalso the SAP particles from coagulating with each other in making theabsorbent sheet of the present invention and, after the absorbent sheetis made, play the role of a binder to bond the SAP particles togetherand the SAP with the substrate fabric. The short-cut staple fibercomponent takes the SAP particles into a network structure incooperation with a supporting sheet by dividing the SAP particlescovered with the HFFM and then covering the SAP particles in a networkform.

A third embodiment of the present invention provides a compositeabsorbent sheet, wherein, in an absorbent sheet provided with a liquidpervious supporting sheet and an absorbent layer containing the SAPparticles as bonded onto either surface of the liquid pervioussupporting sheet, the absorbent layer forms a plurality of highabsorbing regions having higher absorbing capability than otherwise asdistributed onto the surface of the liquid pervious supporting sheet ina desired pattern.

In the composite absorbent sheet of the present invention, a liquid suchas discharged liquid exudates, when it comes into contact with surfaceof the liquid pervious supporting sheet of an absorbent sheet, i.e., thesurface where no absorbent layer exists, is first absorbed by the liquidpervious supporting sheet, penetrates inside the sheet by virtue of theliquid permeability, then diffuses, and contacts and is absorbed by anabsorbent layer provided in contact with the opposite side of thesurface where the liquid was discharged. The speed of absorption of theabsorbent sheet as a whole is determined by the speed of absorption anddiffusion into the liquid pervious supporting sheet and by the speed ofthe swelling and the absorption which occur in succession from thesurface of the absorbent layer into its inside.

Therefore, if there is any difference in the thickness or density of theabsorbent layer, as a liquid is discharged, the swelling and absorptionprogress first from thinner regions or regions of lower density. Also,if there is any difference in particle diameter of the SAP particlescontained in the absorbent layer, the swelling and absorption progressfirst from regions of smaller diameters of particles. A basic concept ofthe present invention is that differences in absorbing capability causedby distributing regions of higher absorbency onto the surface of anabsorbent sheet in a desired pattern are made to be reflected indifferences in swelling and absorbing speeds.

In addition, by giving irregularly shaped circumference to the absorbentlayer, the length of the circumference is made much longer than astraight or simply curved line of the circumference which would be ifthe irregular shape were not given, and therefore, a liquid onceabsorbed by the supporting sheet is absorbed rapidly by the absorbentlayer having the long contact line so that the absorbing speed is thusfurther improved.

In order to distribute and form in a desired pattern the componentforming the absorbent layer onto the supporting sheet, a method ofmaking the component a slurry and applying and fixing the slurry ontothe supporting sheet in a desired pattern meeting objectives iseffective. The method needs to consist of a dispersing step where aslurry dispersion liquid containing the SAP particles is prepared, of acoating step where the dispersion liquid prepared in the dispersing stepis applied onto the surface of the liquid pervious supporting sheet toform a plurality of regions of higher absorption distributed in adesired pattern and having higher absorbing capability than otherwise,and of a drying step where the absorbent layer formed in the coatingstep is dried.

In addition, the present invention provides an apparatus for working themethods. The apparatus comprises a plurality of nozzles for applying adispersion slurry liquid containing the SAP particles in bands ontoeither surface of a liquid pervious supporting sheet runningcontinuously and a supplying means for supplying the dispersion slurryliquid to the nozzles, and is characterized in that the supplying meanshas a mechanism of pulsating the flow of the dispersion liquid.

The present invention further provides an apparatus for making anabsorbent sheet wherein a plurality of nozzles for applying a dispersionslurry liquid containing the SAP particles in bands onto either surfaceof a liquid pervious supporting sheet running continuously and asupplying means for supplying the dispersion slurry liquid to thenozzles are provided, and wherein the nozzles each have a plurality ofdischarging outlets.

The apparatus can be provided with a hot pressing means for pressing theliquid pervious supporting sheet as heated after a dispersion slurryliquid is applied.

A fourth embodiment of the present invention provides an absorbent tube,wherein the absorbent tube is composed of a supporting sheet consistingof a fiber web and the SAP particles or fibers supported by eithersurface of the supporting sheet, and wherein the supporting sheet isformed in a tube shape with the surface supporting the SAP facinginside.

The absorbent tube of the present invention has a novelthree-dimensional structure, wherein a space for the SAP to swell isprovided as the inherent structure of the absorbent by forming a tube ofan absorbent sheet supporting the SAP.

In the absorbent tube of the present invention by virtue of the abovedescribed structure, an absolute quantity of the SAP existent in a unitarea is approximately two times as much as that of an absorbent of aplane structure, and the absorbing capability of a unit area is alsoapproximately two times as high as that of an absorbent of a planestructure. In addition, in the absorbent tube of the present invention,because the SAP is supported as attached onto the inner wall of a tubeshaped supporting sheet, an adequate space for swelling is secured, andeven if the SAP has swollen to its maximum absorbing capabilityabsorbing a liquid, the absorbent as a whole still maintains itsflexibility.

Various types of absorbent sheets have been spreaded so far. In order tomake the function of an absorbent as used in an absorbent productexhibit to its maximum, the absorbent before it absorbs a liquid needsto be very thin like an underwear so that a sufficient space forswelling needs to be provided not to prevent the swelling of theabsorbent. The present invention satisfies the need adequately, andprovides an absorbent exhibiting an outstanding absorbing capability asassisted by the capability of a supporting sheet to diffuse a liquid.

The present invention further provides an absorbent product, wherein anabsorbent tube consisting of a highly absorbent composite having athree-dimensional structure as described in the above is disposed inregions of desired absorptions as an absorbent core. The absorbent tubeof the present invention is flat as not yet swollen and extremely thinlike a crushed flat hollow tube, and when swollen absorbing water risesup as it as a whole swells with the cross-section area showing a nearlycircular shape for the inside vacancy is filled with the SAP whichincreases in volume as swollen. In the absorbent product of the presentinvention, a single absorbent tube may be disposed in the absorbingregion, but more preferably, a plurality of absorbent tubes are disposedin parallel. In the latter case, the structure is more stable and moreflexible, and may more smoothly follow the body movement of the wearerof the absorbent product.

A fifth embodiment of the present invention provides an absorbent sheet,wherein a liquid impervious sheet material one of whose surfaces hasmany dents and absorbent material received and fixed in the dents areprovided and thus leakage resistance and absorbing capability areimparted at the same time. In this embodiment of the present invention,the absorbent composite forms a structure where in the many dentsprovided on one of the surfaces of a liquid impervious sheet material,absorbent material containing absorbent polymer particles is filled. Thecomposite absorbent has leakage resistance and absorbing capability atthe same time satisfying the following requirements:

(1) A liquid impervious sheet material having dents on its surface, and,preferably, air permeability as well as water proofing is used.

(2) Absorbent material having such absorbing capability that is as highas possible is used.

(3) Absorbent material is filled and fixed in the dents.

The commonest form of material having a structure of dents as used inthe present invention is flexible thermoplastic film such aspolyethylene, polypropylene, and EVA of approximately 5 to 50 micronthickness on which many holes or recesses of given shapes are formed bymechanical punching, thermal forming, vacuum forming, or the like.Liquid impervious sheet material can also be used effectively andefficiently part of which has openings formed which are filled withabsorbent material, to be described later, so that water proofing andleakage resistance are imparted.

Absorbent material to fill the dents needs to be of fine sizes to fill arelatively small space, and at the same time to have a high absorbingcapability per a unit volume to secure a required absorbency with thequantity of the material to fill the small space.

The liquid impervious sheet material is, for example, thermoplastic filmof 5 to 50 micron thickness, or a conjugate of 5 to 50 thickthermoplastic film and non-woven fabric. The dents formed on the sheetmaterial may have the same liquid imperviousness as otherwise, or, analternative configuration is that, in the bottoms of all or part of thedents, opening or porous portions which, as they are, liquid may passthrough may exist and are stopped up with the absorbent material. Theabsorbent sheet of this configuration is liquid impervious as a whole,and at the same time, with the absorbent material received and fixed inthe recesses, exhibits a high liquid absorbing capability so that itcombines the two functions of a liquid impervious sheet and anabsorbent.

As a method of filling and fixing the dents provided on a liquidimpervious sheet material with the SAP or absorbent material containingthe SAP, a method generally applied in making absorbents for use indiapers and sanitary napkins can be applied as it is. One preferablemethod comprises the steps of dispersing, for example, the SAP and theHFFM in air current, of filling the dispersed materials into the dents,and of fixing the filled dents by means of hot melt.

If each and every dent on a liquid impervious sheet material is providedwith an opening or liquid pervious structure, by supplying the liquidimpervious sheet material onto a conveyor with a vacuum provided andsupplying the slurry from above the liquid impervious sheet materialcontinuously, the liquid contained in the slurry passes the sheetmaterial through the opening or liquid pervious structure to beseparated, leaving only the solid component in the slurry in the dents.Further, by removing the liquid component and drying, the SAP particlesor the SAP particles and the sheet material are bonded by the HFFM witheach other, and fixed in the positions that they are situated, so thatwater proofing is imparted, too. By selecting an appropriate ratiobetween the quantity of the SAP and the quantity of the HFFM as well asthe properties of the HFFM, preferable properties can be imparted asmaterial for an absorbent: while desired leakage resistance and some airpermeability are obtained at the same time.

The SAP which is used for these purposes should be particles,preferably, fine particles, so that it may be held stably in a smallspace, and specifically, the diameter of the particles should be 0.4 mmor less, or, more preferably, 0.3 mm to 0.1 mm. Very fine particles,such as those of 0.1 mm diameter, can be coexistent with coarserparticles, such as those of 0.4 mm or coarser. In case fiber materialsuch as wood pulp is made to coexist with the SAP, the more the contentof the SAP, the better the result: the content of the SAP is preferably50 percent or higher.

As discussed in the above, in making the composite absorbent of thepresent invention, the HFFM, the SAP and, as required, a short-cutstaple fiber component are dispersed in a dispersion medium. Aparticularly effective dispersion medium is a polyvalent alcohol, whichhas the tendency to be highly viscous at a low temperature andlogarithmically to reduce in viscosity as heated. Specifically, byutilizing the behavior in the relation between temperature and viscosityof a mixed system of a polyvalent alcohol and water, the transferringand forming are carried out while the system is stably maintained whichis made at a low temperature and highly viscous at the time ofdispersion and storing, and the forming and removal of the liquidcomponent are made easier while the system is heated and hydrated at thetime of removing the liquid component so that the viscosity is decreasedand the liquidity is increased.

DETAILED DESCRIPTION OF THE INVENTION

Hereunder, the elements constituting each structure of the highlyabsorbent composite and the absorbent sheet provided with the absorbentcomposite of the present invention will be described.

In a first aspect of the present invention, the absorbent composite iscomposed of the SAP and the HFFM.

In a second aspect of the present invention, the absorbent composite iscomposed of the SAP, the HFFM, and a short-cut staple fiber component,which is larger than the SAP.

In a third aspect of the present invention, either of the absorbentcomposites of the first and the second aspects forms an absorbent sheetcombined with a supporting sheet.

If components are extracted from these absorbent composites and theseabsorbent sheets to be made by combining the absorbent composites, thefollowing four components will come out.

First of all, each component will be described:

(1) SAP Particles

Absorbent polymer particles, herein called the “SAP”, are generallycarboxy methyl cellulose, polyacrylic acid and polyacrylates,cross-linked acrylate polymers, starch-acrylic acid grafted copolymers,hydrolysates of starch-acrylonitrile grafted copolymers, cross-linkedpolyoxyethylene, cross-linked carboxymethyl cellulose, partiallycross-linked water swellable polymers such as polyethylene oxide andpolyacrylamide, isobutylenemaleic acid copolymer, etc. Base polymerparticles are obtained by drying any of these polymers. Then, aftertreatment is applied to increase the cross-linking density of thesurface of the particles, and at the same time, a blocking inhibitor isadded to control the blocking of product particles due to absorbingmoisture.

Also, an amino acid cross-linked polyaspartic acid which isbiodegradable or a microorganism based highly absorbent polymer which isa cultured product of Alcaligenes Latus is added, too.

SAP products are available on the market in such forms as particles,granules, films, and non-woven fabrics. The SAP product in any of suchforms can be used in the present invention. A preferable SAP product forthe present invention is in such forms as particles, granules, pellets,flakes, short needless and the like which can be uniformly dispersed ina dispersion medium. In this specification of the present invention, theterm “particle(s)” is used to generally mean any of these forms.

(2) HFFM

In the present invention, a micro-network structure holding the SAPparticles in position is fixed with the HFFM. The structure prevents theSAP particles from coagulating with each other, and stabilizes and makesuniform dispersion condition in making the composite absorbent of thepresent invention, and serves as a binder for binding the SAP particleswith each other and the SAP with a supporting sheet after drying iscarried out.

The HFFM is, in general, extremely fine fibrous material of 2.0 to 0.01microns in average diameter, and of 0.1 microns or finer on average, andsufficiently water resistant to prevent the structure from collapsingimmediately after or when the SAP absorbs water and so swells, andbesides, has such properties as do not hinder the permeability of waterand the swelling of the SAP. What is specially noteworthy here is thatthe HFFM has an extremely strong hydratable property of binding withwater. By virtue of the strong hydratable property, the HFFM hydrateswhen dispersed in a medium containing water to show a high viscositywhich serves to maintain a stable dispersion condition.

A characteristic of the hydrating property of microfibril is a highamount of retained water. For example, the desired hydrating property ofmicrofibril after their dispersion is centrifuged at 2,000 G for 10minutes as calculated by the following formula should be 10 ml/g orhigher, and preferrably 20 ml/g or higher:Amount of water retained (ml/g)=Precipitated volume (ml)/Microfibrils(g)

In this specification of the present invention, the term “HFFM” is usedto mean generally strongly hydratable fibrous materials in the form ofmicrofibril. In some cases, the HFFM of 2.0 microns or larger in averagediameter can be used, and may be a mixture of so-called fibrils and theHFFM.

The HFFM can be obtained by microfibrillating cellulose or a cellulosederivative. For example, the HFFM is obtained by grinding andsufficiently beating wood pulp. The HFFM is called “microfibrillatedcellulose (MFC)”, and if further fibrillated, is called “supermicrofibrillated cellulose (S-MFC)”.

Also, the HFFM can be obtained by grinding and sufficiently beatingfinely cut fiber of man-made cellulosic fiber such as Polynosic modifiedrayon staple fiber, Bemberg cuprammonium rayon yarn, and solvent spunLyocell rayon fiber.

Alternatively, the HFFM can also be obtained by metabolizingmicroorganism. In general, acetic acid bacteria such as AcetobactorXylinum is cultivated, while stirred, in a nutrient containing anappropriate carbon source so as to generate crude HFFM, which is in turnrefined to obtain the HFFM. Such HFFM is called “bacteria cellulose(BC)”.

Also, so-called fibril type material which is obtained by coagulatingunder a shear force a copper ammonium solution of cellulose, an amineoxide solution of cellulose, an aqueous solution of cellulose xanthate,or an acetone solution of cellulose, all of which can be spun intofibers, is refined to obtain microfibril-type material, which materialcan also be used for the present invention. The details of the HFFM aredescribed in Japanese Patent Examined Publication Nos. SHO 48-6641 andSHO 50-38720.

Such HFFM is commercially available under trademarks “CELLCREAM” (madeby Asahi Chemical Industry Co. Ltd.), “CELLISH” (made by Daicel ChemicalIndustries, Ltd.), and so forth.

MFC, S-MFC, and BC are particularly preferable for the presentinvention. The technical details of the S-MFC are described in JapanesePatent Publication No. HEI 8-284090, and of the BC in Japanese PatentExamined Publicaion No. HEI 5-80484.

How to use the MFC and the S-MFC, (both being hereinafter referred to asthe “MFC”) is explained in detail below. The MFC which is concentratedto approximately 30 percent of solid content is available on the market.To use such concentrated MFC, an additional procedure of diluting andrefining such MFC is required, which requires an additional time, andthe concentrating needs an additional cost. For the present invention,the MFC whose concentrated solid content is 10 percent or lower ispreferable. However, if the MFC is diluted to 2 percent or lower, thewater content will become too high, and the selection of the contents ofthe MFC in an organic solvent/water mixture system will, be too narrow.In case the MFC in a diluted system like this is used, it is recommendedthat an organic solvent/water system in which an organic solvent to beused in a dispersion medium is used rather than a simple water system inmicrofibrillating raw material pulp. Hence, a dispersion liquid of theMFC which is diluted to around 2 percent can also be used for thepresent invention.

How to use the BC is also described in detail below. The BC is obtainedas a metabolized product of microorganism. Depending on the methods ofcultivating and harvesting, the concentrations and the forms of the BCwill be different. In order to obtain as uniform concentrations andforms as possible, a refining treatment is recommended. Maceratingharvested and refined BC which is diluted to 2 percent or lower by meansof a mixer or a defibrator will make finer and more uniform HFFM incoagulated condition, and its viscosity will be much increased and itscapacity of binding the SAP will also be improved. For the presentinvention, therefore, the use of the BC which is refined is recommended.

(3) Short-Cut Staple Fiber Component

The preferable denier of short-cut staple fibers constituting ashort-cut staple fiber component is 10 or more times as coarse as thatof the MFC. The average denier is preferably approximately 0.01 denieror coarser and approximately 3.0 denier or finer.

In the present invention, the length of short-cut staple fibersconstituting a short-cut staple fiber component is an important element.The short-cut staple fibers which are to divide in sections the SAPparticles covered by the MFC and to cover the particles in a networkstructure need to have longer fiber length than the average diameter ofthe SAP particles. In general, the average particle diameter of the SAPavailable on the market is approximately 0.1 mm to 0.6 mm.

The SAP which is made by dispersion polymerization has relatively smallparticle diameter. If such SAP is used, short-cut staple fibers whichare relatively short can adequately be used. On the hand, if the SAP inpelletized or flake form is used, short-cut staple fibers which arerelatively long should preferably be used.

These short-cut staple fibers play the role of covering swollen SAP. Ifthe short-cut staple fibers swell or dissolve in the same way as theSAP, they will not be effective. The short-cut staple fibers, therefore,need to have a property that they will not swell or dissolve in water.

The short-cut staple fibers which can be effectively used for thepresent invention are grouped into the following two kinds:

(i) Pulp State Fibers

Typical pulp fibers are wood pulp obtained by digester reclaimingneedle- or broad-leaved trees, linter pulp obtained with cotton linteras raw material, or the like. Other pulp state fibers are obtained byshear coagulation, flush spinning, or spray spinning of polymersolutions to make solidified fibers: acetate (ACe) fibril,polyacrylonitrile (PAN) fibril, polyethylene (PE) based synthetic fiberpulp, polypropylene (PP) based synthetic fiber pulp or the like areavailable. In addition, in case fine SAP is used, pulp state fiberobtained from strained lees of beet or coffee beans can also be used asthe short-cut fibers. PP and PE based synthetic fiber pulps are easy tothermally melt, and as such preferably used to make more stablestructure by thermal treatment.

(ii) Short Cut Synthetic Fibers

-   -   Of cellulosic fibers such as rayon, Polynosic modified rayon,        and Lyocell, short-cut staple fibers and their fibrillated        materials of 10 mm or shorter in fiber length made for making        paper.    -   Short-cut staple fibers such as PET, PP, PVA, and PAN, and        short-cut staple fibers of bicomponent fibers such as low        melting point polyester/PET, PP/PE, and PE/PET.    -   Short-cut fibers of very fine fibers obdtained by blending of        different polymers, or by spinning is land-like fibers.

Particularly, bicomponent fibers such as PE/PET, PE/PP, and low meltingpoint polyester/PET are preferable to aim at stabilizing the SAP by heattreatment through utilizing the effects of the component in thecompositefibers that is easy to thermally dissolve. Also, those of such fibers onwhich an antibacterial agent or a deodorant is applied are preferable.

(4) Supporting Sheet

A supporting sheet functions as follows: through binding the SAPparticles covered and bonded by the MFC to a supporting sheet, thestrength and dimensional stability are improved, and the liquid to beabsorbed through the supporting sheet is diffused and distributed, andthe SAP particles are stopped up in the dents, raised fibers, entangledfibers, or vacancies which are likely to exist on the supporting sheetso that the stability is achieved.

The supporting sheets which can be used for the present invention aredescribed in detail here: In the present invention porous sheets such asdry laid fluff pulp mat and its bonded sheet, wet formed pulp mat,carded dry laid non-woven fabric, spun lace, spunbond, melt-blownnon-woven fabric, and non-woven fabric made of opened tow of acetate orpolyester fibers can be used. A supporting sheet is preferably of abulky structure to hold and stabilize the SAP particles in its spaces.As for the bulkiness of the supporting sheet, an apparent density ascalculated from a thickness measured using a thickness gauge (asdescribed later) and a weight should be 0.2 g/cm³ or less, andpreferably 0.1 g/cm³ or less.

To obtain such bulky non-woven fabric, the following means are taken:

<Web Comprising a Combination of Finer Denier Fibers and Coarser DenierFibers>

While coarser denier fibers are high in resilience and compressionresistance, but a web of such coarser fibers is not high in bondingstrength, finer fibers give the opposite tendency. Therefore, it ispreferable to combine both types of fibers. Such combination is obtainedby blending coarser denier fibers and finer denier fibers or laying alayer of coarser denier fibers on top of a layer of finer denier fibers.To achieve an object of the present invention, a two-layer structure,particularly, a non-woven fabric comprising a combination of a layer ofhydrophilic fibers which are relatively high in density and of finerdenier and a layer of hydrophobic fibers which are relatively low indensity and of coarser denier, is preferable.

<Non-Woven Fabric Given Bulkiness>

In addition to combining fibers of different deniers, shrinkable fiberscan be combined. By shrinking such shrinkable fibers, an uneven surfacehaving dents or a corrugated surface having furrows is made, which is amethod of making a bulky supporting sheet as is suitable for the presentinvention.

<Bulky Supporting Sheet Whose Surface is Treated>

By flocking a non-woven fabric of a smooth surface or raising arelatively thick non-woven fabric mechanically, a bulky supporting sheetsuitable for the present invention can be made.

The composite absorbent sheet of the present invention comprising theabove-described four components is required to have the followingstructure in order to fully exhibit the functions as are expected of anabsorbent sheet: the sheet needs to have a stable structure so that whenit is dry it can be folded, slitted and stretched to extend, and formedto be corrugated, and when it is worn to absorb body exudates, it needsto have outstanding absorbing and diffusing capabilities, and after itis used, no SAP particles should exfoliate or come off.

Even if the absorbing rate is high, the sheet should not have suchstructure which may collapse. On the other hand, even if the SAPparticles are stably fixed, if the sheet takes a long time to absorb andswell, it will not be suitable for the present invention. Hence, animportant requirement of the present invention is how best theabove-described four components are combined in a rational way. (5)Combinations of the four components

Next, various combinations of the four components and their advantagesare described in detail below:

(a) Combination of Supporting Sheet and Short-Cut Staple Fibers

Whether a supporting sheet is hydrophilic or hydrophobic determinesdesirable properties of short-cut staple fibers to be used incombination with the supporting sheet. That is to say, in case thesupporting sheet is of hydrophobic fibers such as PP and PET, short-cutstaple fibers to be combined with the supporting sheet are preferablycellulosic fibers such as wood pulp and fibrillated Lyocell. By usingsuch fibers, the absorbency and diffusion will be much improved. On theother hand, in case hydrophilic fibers such as rayon are used, theyshould be combined with PE synthetic pulp, or short cut PE/PETbicomponent fibers, which will maintain a preferable balance between theabsorbency and diffusion and the retention of form.

(b) Combination of supporting sheet and heat meltable short-cut staplefibers

To obtain a good wet stability of an absorbent sheet, heat setting acombination of a supporting sheet of a specified structure withshort-cut staple fibers is preferable, which makes it possible to obtaina strong structure.

For example, if a carded web of 15 g/m² consisting of 1.5 denier rayonfiber and a carded web of 15 g/m² consisting of 6 denier PET fiber arewater-jet entangled, then a web of a two layer structure having astrongly hydrophilic bottom layer and a bulky top layer is obtained. Onthe other hand, by dispersing a short-cut staple fiber (a bicomponentfiber of PET/low melting point polyester which is easy to heat melt, of1.2 denier and 2 mm fiber length) in the MFC/SAP slurry, a co-dispersedslurry is obtained, and by spreading this co-dispersed slurry onto thePET layer of the two layer web, a solid layer is obtained. Next, bydrying and then heat setting this solid layer, a network structure wherePET of the supporting sheet and easy to heat melt polyester, of theshort-cut staple fiber component are thermally fused is formed, in whichnetwork structure the SAP particles are contained in closed spaces.

In a structure like this, when liquid is absorbed, the liquid is rapidlysupplied from the hydrophilic supporting sheet layer to the SAPparticles to start swelling, and even after sufficiently swollen, theSAP will hardly come off the supporting sheet. The kinds of fibersforming the bulky layer of the non-woven fabric of a two layer structureand the combinations with the short-cut staple fibers suitable to suchbulky layer fibers are shown below:

Bulky fiber component of a supporting sheet Short-cut staple fibercomponent of a two layer structure to be added as slurry Coarser denierPE/PET PE synthetic pulp, finer denier PE/PET Coarser denier PE/PET PEsynthetic pulp, finer denier PE/PET Coarser denier PET Finer denierPET/easy-to-melt polyester Coarser denier RayonEasily-soluble-in-hot-water PVA fibers(c) Blending Ratio of MFC and Short-Cut Staple Fibers

In general, short-cut staple fibers are added to a slurry of the MFC toprovide a two-component dispersion liquid, and, the SAP particles areadded further to provide a three-component slurry. The three componentslurry is spreaded onto a supporting sheet. In the three-componentslurry, if the ratio of short-cut staple fibers to the MFC in quantityis too high, the MFC will be used only to cover and bond the short-cutstaple fibers and decrease the bonding efficiency of the SAP, and thestability of the slurry becomes lower. On the other hand, if thequantity of short-cut staple fibers is too small, the desired networkfunction will not be obtained. The ratio of the MFC (P) and short-cutstaple fibers (Q) ranges between P/Q=1/5-5/1, and preferablyP/Q=1/3-3/1.

In the present invention, as described in the above, the threecomponents, the SAP, the HFFM, and a short-cut staple fiber component asrequired, are dispersed in a dispersion medium. The dispersion medium isdescribed below:

To handle the SAP particles and the HFFM, and as required, a short-cutstaple fiber component as a stable slurry-like dispersion liquid, it isimportant to select an appropriate dispersion medium. If the SAP isslurry-like already from the beginning of its making process, forinstance, in a system such as a dispersion polymerization of acrylicacid where polymerization reaction is run in a cyclohexane/water system,by cross-linking in dispersion (if necessary) after polymerizationreaction is finished and then adding to the slurry a water dispersionliquid of the HFFM or a solvent/water dispersion liquid while the liquidis stirred, a stable slurry containing partially swollen SAP and theHFFM can be obtained.

To obtain a stable dispersed slurry using dry SAP available on themarket and the HFFM, and as required, the short-cut staple fibercomponent, it is preferable to disperse them in a mixture medium ofwater and an organic solvent.

If the SAP particles, the HFFM, and as required, the short-cut staplefiber component are dispersed in a dispersion medium like thisconsisting of an organic solvent and water, a dispersion liquid wherethe HFFM and the SAP particles are uniformly and stably dispersed isobtained owing to the viscosity generated by the combination of the HFFMand the dispersion medium.

As organic solvents used for the present invention, alcohols such asmethanol, ethanol, and isopropyl alcohol, polyvalent alcohols such asethylene glycol, diethylene glycol, propylene glycol, low molecularweight polyethylene glycol, and glycerin, and representative watersoluble organic solvents such as acetone, methyl ethyl ketone, dioxane,and dimethyl sulfoxide are available. In using low boiling pointalcohols, an apparatus may need to be of an explosion proof constructionbecause of their high volatility and flammability. On the other hand,ethanol and propylene glycol are preferable because of their safety tothe environment and to the skin of a wearer and low possibility ofremaining in a product. To any of these solvents, a water insolublesolvent such as cyclohexane may be added in a quantity that does notinterfere with dispersion.

As a dispersion medium used to maintain a condition where the HFFM, theSAP particles, and as required, the short-cut staple fiber component areuniformly dispersed, without being coagulated and settling, for arelatively long period of time, solvents of a group of polyvalentalcohols are particularly preferable. Solvents of a group of polyvalentalcohols are water soluble, and do not ice even below 0° C. or lower asare mixed with water showing a highly viscous condition, and thus can bestably stored for some time. As the temperature goes up, the viscositywill decrease, which makes easier the transfer by means of a pump andforming of the composite sheet.

Examples of polyvalent alcohol solvents are ethylene glycol, propyleneglycol, diethylene glycol, triethylene glycol, low molecular weightpolyethylene glycol, and glycerin. The viscosity of the polyvalentalcohol solvents will vary with the temperature very much. For example,as shown in Table 1 below, the viscosity greatly changes for thedifference of 30° C. between 20° C. to 50° C.

TABLE 1 Viscosity (cp) Solvents 20° C. 50° C. Ethylene glycol 22.0 7.3Propylene glycol 56.0 8.6 Diethylene glycol 30.0 11.5 Triethylene glycol49.0 14.0 Glycerine 1412.0 142.0

A manufacturing process can be efficiently designed throughincorporating this change in viscosity successfully in the process.However, a drawback of polyvalent alcohol solvents is that, because theyshow a high viscosity even when they contain water, they may causeuneven coating in coating a substrate sheet material because they do notfit well with the substrate material due to their hardly penetrating thematerial. In such case, adding of methanol or ethanol to combine withthis polyvalent alcohol solvent, for example, applying of athree-component system, PG/ethanol/water, may be effective.

The slurry obtained in the way described in the above which consists ofthe SAP particles, the HFFM, and as required, a short-cut staple fibercomponent forms an absorbent layer as applied on the surface of a liquidpervious supporting sheet. In general, the slurry is applied onto thewhole surface of the absorbent sheet uniformly and evenly, but dependingupon the uses, can be applied in an appropriate pattern.

In the event that the absorbent layer is formed in a pattern, a liquidpervious supporting sheet is a substrate supporting the absorbent layerand concurrently, plays the role of solid-liquid separating from theslurry in the manufacturing process. It is, therefore, preferable thatthe components of a supporting sheet have affinity to an absorbent layerand that at the same time the supporting sheet is of a structure havingfine openings through which solid does not permeate, but liquid doespermeate. For this purpose, a non-woven fabric made of natural fiber,chemical fiber and synthetic fiber provides a preferable supportingsheet. Especially, in case the HFFM of cellulose fiber is used as abonding agent, cellulose fiber which has a bonding to hydrogen ispreferably combined to make a supporting sheet.

In the present invention, an absorbent layer is formed by applying theabove-described slurry onto the surface of a liquid pervious supportingsheet, and it is required that as a result of such application of theslurry a plurality of highly absorbing regions having higher absorbingcapability distributed in a desired pattern need to be formed.

A representative means of forming an absorbent layer as non-uniformlydistributed is to form a distribution in a pattern by pulsating in someappropriate way the discharging quantity or width of a slurry dispersionliquid or to form the absorbent layer yet to be solidified after theslurry is applied.

Means for pulsating the dispersion liquid as discharged is to use aplunger pump or a tube pump which discharges the liquid with pulsation.When a pump which does not pulsate the quantity of discharge is used, adevice of giving pulsation needs to be installed at the side ofdischarging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between the concentration andthe viscosity of the HFFM in a solvent;

FIG. 2 is an explanatory diagram showing a process of obtaining the HFFMfrom cellulose;

FIG. 3 is a graph showing the concentration of an organic solvent andthe swelling rate of the SAP in a dispersion medium;

FIG. 4 is a graph showing the relationship between the viscosity ofethylene glycol and of propylene glycol and the temperature from minus10° C. to 100-140° C.;

FIG. 5 is a graph showing the relationship between the viscosity ofpropylene glycol and the temperature in an aqueous solution for thecases of mixing ratios of 4/6, 6/4 and 812;

FIG. 6 is an explanatory diagram showing a concept of forming variousabsorbent composites from slurry dispersion liquids;

FIG. 7 is a sectional view of an absorbent composite embodying thepresent invention; FIG. 7( a) shows an absorbent composite in particles,and FIG. 7( b) shows an absorbent composite in flake;

FIG. 8 shows a sheet material consisting of an absorbent compositeembodying the present invention; FIG. 8( a) is a schematic sectionalview and FIG. 8( b) is a sketch of a microphotograph thereof;

FIG. 9 shows another sheet material consisting of an absorbent compositeembodying the present invention; FIG. 9( a) is a schematic longitudinalsection and FIG. 9( b) is a sketch of a microphotograph thereof;

FIG. 10 is a schematic longitudinal sectional view of a composite sheetmaterial embodying the present invention;

FIG. 11 is a longitudinal sectional view of a composite sheet materialembodying the present invention;

FIG. 12 is a longitudinal sectional view of a composite sheet materialembodying the present invention;

FIG. 13 is a longitudinal sectional view of a composite sheet materialembodying the present invention;

FIG. 14 is a partial perspective view of a composite sheet materialembodying the present invention;

FIG. 15 is a longitudinal sectional view of a composite sheet materialembodying the present invention;

FIG. 16 is an explanatory drawing typically showing an example of anabsorbent sheet having a distribution of patterns;

FIG. 17 is an explanatory drawing typically showing another example ofan absorbent sheet having a distribution of patterns;

FIG. 18 is an explanatory drawing typically showing still other exampleof an absorbent sheet having a distribution of patterns;

FIGS. 19(A), (B), (C) and (D) are longitudinal sectional views ofdifferent forms of an absorbent tube embodying the present invention;

FIG. 20(A) is a sectional view of an absorbent sheet which can be usedfor the present invention, and FIG. 20(B) is a cross sectional view ofan absorbent tube consisting of the absorbent sheet of FIG. 20(A);

FIG. 21(A) is a sectional view of an absorbent sheet which can be usedfor the present invention, and FIG. 21(B) is a cross sectional view ofan absorbent tube consisting of the absorbent sheet of FIG. 21(B);

FIG. 22 is a cross sectional view of another example of an absorbenttube of the present invention;

FIG. 23 is a plan view of an example of an absorbent product of thepresent invention;

FIG. 24 is a fragmentary sectional view taken along section line A-A ofFIG. 23;

FIG. 25 is a sectional view of another absorbent product of the presentinvention as shown in the same way as in FIG. 23;

FIG. 26 is a sectional view of other absorbent product of the presentinvention as shown the same way as in FIG. 23;

FIG. 27 is a sectional view of still other absorbent product of thepresent invention as shown in the same way as in FIG. 23;

FIG. 28 is a sectional view of an absorbent tube, as swollen, used inthe absorbent product of the present invention as shown in FIG. 24;

FIG. 29 is a sectional view of still other absorbent of the presentinvention as shown in the same way as in FIG. 23;

FIG. 30 is a sectional view of still other absorbent of the presentinvention as shown in the same way as in FIG. 23;

FIG. 31 is a cross sectional view of other example of the absorbent tubeof the present invention;

FIG. 32 is a cross sectional view of other example of the absorbent tubeof the present invention;

FIG. 33 is a cross sectional view of other example of the absorbent tubeof the present invention;

FIG. 34 is a cross sectional view of other example of the absorbent tubeof the present invention;

FIG. 35 is a cross sectional view of other example of the absorbent tubeof the present invention;

FIG. 36 is a sectional view of a supporting sheet which can be used toconstitute the absorbent tube of the present invention;

FIG. 37 is a sectional view show the condition where the SAP particlesare carried and held by the supporting sheet of FIG. 37;

FIG. 38 is a fragmentary sectional view of an absorbent productconstituted by using an absorbent tube having the structure of FIG. 37;

FIG. 39 is a partial perspective view of a porous liquid impervioussheet constituting the absorbent of the present invention;

FIG. 40 is a plan view showing a part of the surface of the absorbentsheet of the present

FIG. 41 is a longitudinal sectional view of the absorbent sheet of FIG.40;

FIG. 42 is a schematic diagram showing a process of making the absorbentsheet of the present invention;

FIG. 43 is a plan view of a liquid impervious sheet material used forthe absorbent sheet of the present invention;

FIG. 44 is a plan view showing the condition where in the recesses ofthe liquid impervious sheet of FIG. 43 absorbent material is filled;

FIG. 45 is a fragmentary plan view showing other absorbent sheet of thepresent invention;

FIG. 46 is a fragmentary longitudinal sectional view of FIG. 45;

FIG. 47 is a fragmentary plan view showing still other absorbent sheetof the present invention;

FIG. 48 is a block diagram showing an example of a process of adding ashort-cut staple fiber component to the HFFM in the present invention;

FIG. 49 is a block diagram showing an example of a process of adding ashort-cut staple fiber component to the HFFM in the present invention;

FIG. 50 is a block diagram showing an example of a process of adding ashort-cut staple fiber component to the HFFM in the present invention;

FIG. 51 is a block diagram showing an example of a process of adding ashort-cut staple fiber component to the HFFM in the present invention;

FIG. 52 is a fragmentary longitudinal sectional view showing anabsorbent sheet of the present invention while it is in dry condition;

FIG. 53 is a fragmentary longitudinal sectional view showing theabsorbent sheet shown in FIG. 52 while it is in wet condition;

FIG. 54 is a fragmentary longitudinal sectional view showing otherabsorbent sheet of the present invention while it is in dry condition;

FIG. 55 is a plan view showing an example of an absorbent sheet of thepresent invention;

FIG. 56 is a fragmentary enlarged sectional view of the absorbent sheetof FIG. 55;

FIG. 57 is a flow chart showing an example of a process of making asupporting sheet to be used in the present invention;

FIG. 58 is an explanatory drawing showing the sectional view of thesupporting sheet made by the process of FIG. 57;

FIG. 59 is a fragmentary hatched plan view showing an example of asupporting sheet suitable FIG. 60 is a fragmentary enlarged sectionalview of FIG. 59;

FIG. 61 is a schematic longitudinal sectional view of an apparatus formaking a composite sheet material according to the present invention;

FIG. 62 is a schematic longitudinal sectional view showing a modifiedexample of the apparatus of FIG. 61;

FIG. 63 is a schematic longitudinal sectional view showing anothercoating apparatus to be used in the apparatus shown in FIG. 61;

FIG. 64 is a plan view of a grooved roll used in the apparatus of FIG.63;

FIG. 65 is a cross sectional view of a supporting sheet which is coatedwith a dispersion liquid by the apparatus shbwn in FIG. 63 and FIG. 64;

FIG. 66 is a perspective view schematically showing an example of anapparatus for making an absorbent sheet of the present invention;

FIG. 67 shows an example of a nozzle for discharging a slurry dispersionliquid to be applied in the apparatus of FIG. 66: (A) is a side viewthereof and (B) is a bottom view thereof;

FIG. 68 shows another example of a nozzle for discharging a slurrydispersion liquid to be applied in the apparatus of FIG. 66: (A) is aside view thereof and (B) is a bottom view thereof;

FIG. 69 is a perspective view showing an example of a nozzle fordischarging a slurry dispersion liquid to be used for making anabsorbent sheet of the present invention;

FIG. 70 is a perspective view showing an example of a nozzle fordischarging a slurry dispersion liquid to be used for making anabsorbent sheet of the present invention;

FIG. 71 is a perspective view showing an example of a nozzle fordischarging a slurry dispersion liquid to be used for making anabsorbent sheet of the present invention;

FIG. 72 is an explanatory drawing showing an example of the conditionwhere a nozzle contacts a liquid pervious supporting sheet;

FIG. 73 is an explanatory drawing showing another example of thecondition where a nozzle contacts a liquid pervious supporting sheet;

FIG. 74 is a schematic flow diagram showing an apparatus for making anabsorbent sheet of the present invention;

FIG. 75 is a schematic flow diagram showing another apparatus for makingan absorbent sheet of the present invention;

FIG. 76 is a schematic flow diagram showing other apparatus for makingan absorbent sheet of the present invention;

FIG. 77 is an explanatory drawing showing a method of measuring astiffness and flexibility (mm);

FIG. 78 is a fragmentary sectional view taken along section line A-A ofFIG. 77;

FIG. 79 is a chart drawing showing a criterion of the bonding stabilityof the SAP;

FIG. 80 is a plan view showing a composite absorbent sheet prepared forincorporating into a sample piece in an example of the presentinvention;

FIG. 81 shows other example of a composite absorbent of the presentinvention: (a) is a plan view thereof and (b) is a sectional viewthereof;

FIG. 82 is an explanatory drawing showing a process of making stillother form of a composite absorbent of the present invention;

FIG. 83 shows an incontinent pad for a woman in which a compositeabsorbent of the present invention is applied: (a) is a plan viewthereof, (b) is a sectional view of the composite absorbent, (c) is aperspective view showing the condition where the composite absorbent of(a) is folded, (d) is a side view of a finished incontinent pad for awoman;

FIG. 84 is a perspective view showing material of an absorbent tube usedin an example of the present invention;

FIG. 85 is a cross sectional view of an absorbent tube constituted bythe material of FIG. 84;

FIG. 86 is a cross sectional view of an absorbent tube used in anexample of the present invention;

FIG. 87 shows an example of setting a viscosity and a temperature ineach area of a process with propylene glycol as an example: (A) is aprocess flow thereof, (B) is a chart showing a fluctuation oftemperature in each area of the process, and (C) is a chart showing afluctuation of viscosity in each area of the process;

FIGS. 88 (A) through (E) each are an explanatory drawing showing anembodiment of how the preparation of a dispersion slurry is carried outin each step leading to a coating header,

FIG. 89 is an explanatory drawing showing, with steam as a source ofheating and hydrating, the order of a process consisting of removal ofthe liquid component by decompression in a liquid phase of a formed SAPsheet containing propylene glycol and removing the liquid component in agaseous phase by hot air drying and fluctuations of propyleneglycol/water composition and of residual quantity of propylene glycol;

FIG. 90 is an explanatory drawing showing a process of applying a slurryonto a supporting sheet in many bands extending in parallel atintervals; and

FIG. 91 is an explanatory drawing showing a process of applying a slurryonto a supporting sheet in many bands extending in parallel in contactwith each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail with reference to theaccompanying drawings.

FIG. 1 is an example showing the concentration and viscosity of supermicrofibrillated cellulose in the form of microfibril (hereinaftersometimes referred to as the “S-MFC”) in a dispersion liquid. It will beunderstood from FIG. 1 that even at low concentration a high viscosityis still maintained. The dispersion liquid of the HFFM exhibits astructural viscosity, and a fluidized orientation is exhibited and theviscosity is reduced when a shear force is applied. However, as theshear force is reduced, the viscosity is restored. Thus, if the SAPparticles are added and dispersed in the dispersion medium of the HFFM,in a low sheared dispersion state, the SAP particles are stably taken ina network structure of the HFFM, and consequently, the SAP of a highconcentration can stably be dispersed. The dispersion is transferredwith ease by means of a pump or the like, because then the viscosity isdecreased.

Therefore, when the SAP is dispersed in a dispersion medium of the HFFM,the SAP of a high concentration can be stably dispersed. In the processwhere the dispersion medium is removed, the HFFM are in a plaster stateto form a network structure as they are firmly self-bonded and containand mechanically enclose the SAP particles, and as the HFFM is bondedwith each other in the effect of hydrogen bonds, hold securely the SAPparticles.

Fine fibers in the form of microfibril (the “HFFM”) can be obtained bymicrofibrillating cellulose or its derivative. For example, by grindingand sufficiently beating wood pulp, the HFFM is obtained in a process asshown in FIG. 2. The HFFM is sometimes referred to as the “MFC”(microfibrillated cellulose) and if further fibrillated, as the “S-MFC”(super microfibrillated cellulose).

Next, a method of making a highly absorbent composite composed of theabove-described HFFM and the SAP is described below:

According to the present invention, in making the above-described highlyabsorbent composite, the dispersion behavior of the SAP in a dispersionmedium of the HFFM and the behavior of the HFFM after removing theliquid component are ingeniously utilized. In other words, the highlyabsorbent composite of the present invention can be obtained bydispersing the SAP particles and the HFFM in a dispersion, medium thatis a mixture of an organic solvent miscible with water and water wherethe HFFM is stably hydrated and dispersed, by separating the SAPparticles and the HFFM from the resultant dispersion liquid, and byremoving the liquid component, followed by drying. As a result of thisprocedure, a typical pulpless highly absorbent composite where thecontent of the SAP is 90 percent or higher can be obtained.

To prepare a dispersion liquid of the HFFM, a dispersion liquid wherethe HFFM is dispersed in water is first prepared as a stock liquid. Asthe concentration of the stock liquid becomes higher, an apparatuspreparing the HFFM dispersion becomes more compact. On the other hand,however, the viscosity of the stock liquid increases at higherconcentrations, which makes the handling of the stock liquid moredifficult. Therefore, a water dispersion liquid with a concentration of10 percent or lower, preferably 5 to 1 percent, is used. The stockliquid is added to a dispersion medium consisting of an organic solventand water to obtain a dispersion liquid of the HFFM having a prescribedconcentration of the HFFM and a viscosity accompanied by theconcentration. As a means of adding and mixing the SAP to the dispersionliquid, a means of dispersing the SAP particles into the above-describeddispersion liquid is generally applied.

By dispersing the HFFM and the SAP in this dispersion liquid of anorganic solvent and water, a network structure of the HFFM is formed andthe SAP particles are incorporated in the network structure so that astable dispersion state is secured. When the dispersion medium isremoved later, the physical entwined structure of the HFFM and thestable hydrogen bonding of the HFFM with each other are formed, and as aresult, it is assumed that a three dimensional structure is formed.

The mixture ratio of an organic solvent and water is established in arange enabling the formation of a network structure of the 1-IFFM andsuppressing as much as possible the absorption of water by the SAP.

Of the above-described organic solvents, representative solvents aredescribed here. In the graph of FIG. 3 is Shown the relationship betweenthe concentration of an organic solvent and the water absorbing ratio ofthe SAP in the case that as such organic solvent methyl alcohol, ethylalcohol, and acetone are used. It is shown in FIG. 3 that in case ethylalcohol or acetone is used, when the concentration of the solvent is 50percent or lower, the water absorbing ratio of the SAP sharplyincreases, and that, in case methyl alcohol is used, when theconcentration is 60 percent or lower, the water absorbing ratio of theSAP sharply increases. It is, therefore, preferable to have a higherconcentration of an organic solvent.

Of the above-described solvents, solvents of polyvalent alcohols aremore viscous, and among them ethylene glycol and propylene glycol arerelatively easy to handle and easily available on the market. FIG. 4shows the relationship between the viscosity and the temperature fromminus 10° C. to 12° C. for both of them. With safety to the environmentand to the persons who wear sanitary material taken into consideration,the most preferable organic solvent is propylene glycol (hereinafterabbreviated as the “PG”).

The above-described solvents are used mainly in mixture with water inthe present invention. An appropriate mixture ratio between water and asolvent needs to be selected in order to prevent coagulation andswelling of the SAP particles and to disperse stably the SAP particleswith the MFC and the short-cut staple fiber component. The mixture ratioof solvent water is approximately 9/1 to 5/5. If water is more than 5/5,the swelling of the SAP is rapidly increased, and if a solvent is morethan 9/1, the MFC starts to settle. The transition region and nature aresomewhat different depending on the kinds of the solvents used. If thePG is taken as an example, a particularly preferable mixture ratio is6/4 to 8/2. FIG. 5 shows the relationship between the viscosity and thetemperature of the PG in an aqueous solution for the mixture ratios of4/6, 6/4 and 8/2. It is shown that, as the content of water increases,the viscosity relatively decreases, and that a difference in viscositycaused by difference in temperature is large even when the solvent is inan aqueous solution.

On the other hand, in order to hydrate and disperse the HFFM stably, itis more advantageous to have higher content of water in a dispersionmedium. Therefore, an appropriate range of the ratio of an organicsolvent/water is 90/10 to 40/60. Note that the ratio varies to someextent depending upon the organic solvents used and the properties ofthe SAP used.

The dispersion concentration each of the SAP and the HFFM in coexistencein this dispersion medium and the ratio in concentration between the SAPand the HFFM are described in more detail below. The concentration ofthe SAP is selected from a range of 60 percent or lower, preferably 50percent to 5 percent from the standpoint of ease to handle, although itmay be somewhat different depending upon the methods of slurrytransportation. A preferable concentration of the HFFM is selected toobtain the bonding strength and the dispersion stability of the SAP. Tomaintain a good dispersion stability, the concentration of the HFFMneeds to be 0.2 percent or higher, preferably 0.3 percent to 1.0percent.

At this concentration of the HFFM, a dispersion medium containing theHFFM exhibits a good dispersion stability. Even after the medium isallowed to stand for a long period of time, no settling occurs.

Experimental results show that, as the concentration of the HFFMincreases, the dispersion stability improves. When the concentration ofthe HFFM was 0.3 percent, no settling occurred for one hour. At theconcentration of 0.5 percent, no settling occurred for 65 hours. Itproves that, with this good dispersion stability, not only the coatingprocedure becomes easier, but also, the HFFM enclose the SAP particlescompletely so that a stable dispersion is realized.

As the ratio of the HFFM to the SAP (MFC/SAP×100(%)) increases, thestrength of the absorbent composite becomes higher, but at the sametime, the absorbent composite hardens to a paper-like hand. Therefore,the ratio of the HFFM to the SAP is preferably 20% or lower. On theother hand, at the ratio of 0.3% or lower, a sufficient bonding strengthcannot be obtained. The bonding strength is evaluated by applying acellophane adhesive tape method for measuring a surface strength. Theresults of applying the method to the evaluation of the bonding strengthshow that more preferable range of the ratio is 5% to 0.5%.

Next, a method of forming a composite from a dispersion liquid which ismade by dispersing the HFFM and the SAP in a dispersion medium isdescribed with reference to the accompanying drawings below. As a methodof forming an absorbent composite from the above-described dispersionliquid slurry, for example, as shown in a conceptual drawing of FIG. 6,(1) by drying a block-like substance obtained by separating the solventfrom the slurry and crushing the substance into particles; compositeparticles with the surface of the SAP covered by the HFFM, cubic-shapedas shown in FIG. 7( a) or flake-shaped as shown in FIG. 7( b), areobtained, (2) if the slurry is poured into a mold made of, for example,a net and solid and liquid components are separated and dried, apellet-, rod-, cylinder-, or corrugated-plate-shaped three dimensionalformed composite is obtained depending upon the mold used, and (3) ifthin film is formed continuously and dried, a composite sheet isobtained.

An absorbent composite obtained in each of the above-described mannershas flexibility depending upon the water content. Therefore, a compositesheet is formed in a mat shape together with fibers, for example, by anair-laid method and the mat is moistened, pressed, and dried so that itcan be reformed into a sheet shaped composite.

Next, a method of directly forming a sheet from a dispersion liquid,which can be widely used, is described in detail. As described in theabove, a network structure of the HFFM, while maintaining a conditionwhere the SAP is stably and firmly held inside, enables the formation ofa very thin layer. In other words, a dispersion liquid where the HFFMand the SAP are dispersed in a dispersion medium is applied onto asuitable flat surface, and a sheet-shaped highly absorbent composite canbe formed which is composed of only the HFFM and the SAP.

A highly absorbent composite of a shape described in the above is shownin FIG. 8( a). In FIG. 8( a), reference numerals 11 and 12 represent theHFFM and the SAP particles, respectively. In fact, as shown in FIG. 8(b) which is a sketch of a microphotograph magnified by 70 times, eachSAP particle is completely covered by the HFFM and at the same time, theSAP particles are taken in a network structure of the HFFM as theadjoining particles are entwined with each other by the HFFM.

Alternatively, when a dispersion liquid is applied onto a suitablesupporting sheet, a highly absorbent composite sheet material composedof the supporting sheet and an absorbent composite layer is obtainedafter the dispersion liquid is dried. When a porous non-woven fabric isused as the supporting sheet, part of the dispersion liquid entersspaces made by the fibers of the non-woven fabric depending upon thedensity of the non-woven fabric, and a composite sheet where non-wovenfabric 13 and the absorbent composite layer 10 are entwined as they arein contact with each other is formed as shown in FIG. 9( a) and FIG. 9(b) which is a sketch of a microphotograph, after the liquid is dried. Apreferable density of the non-woven fabric is 0.2 g/cm³ or lower interms of the apparent specific density, and, more preferably, 0.01 to0.1 g/cm³.

Preferable fibers constituting the non-woven fabric are, from aviewpoint of the permeability of a liquid, a hydrophilic material suchas cotton, rayon and wood pulp or synthetic fibers treated to behydrophilic such as polyethylene, polypropylene and polyester. Inparticular, the HFFM which is of the S-MFC or the BC has a very stronghydrogen bonding strength in addition to being easily entangledphysically. Therefore, when a cellulosic supporting sheet is used, suchHFFM is more strongly and stably bonded with each other and with thesupporting sheet in a dry state, and exhibits an outstandingpermeability in a wet state.

In addition, in a structure as shown in FIG. 9, other sheet material 14can be bonded in contact with the highly absorbent composite layer 10 asagainst the non-woven fabric 13, as shown in FIG. 10. If, as this othermaterial 14, a liquid impervious sheet material is used, the compositesheet of FIG. 10 alone may have the function of an absorbent product 1composed of a topsheet, an absorbent, and a backsheet.

Furthermore, in the structure of FIG. 9, a highly absorbent compositelayer can be provided not only on the whole front surface of asupporting sheet, but also partially in a desired pattern. For example,as shown in FIG. 11, a plurality of the absorbent composite layers 10are provided in bands of a desired width at prescribed intervals only oneither surface of the supporting sheet 13, with the composite supportingsheet folded in between the adjoining absorbent composite layers in azigzag pattern. Since a composite sheet of this structure has a largervolume of the absorbent composite layer 10 per unit area than a flatcomposite sheet, and accordingly a higher absorbing capability than thelatter. Alternatively, as shown in FIG. 12, when the top portions of thezigzag pattern are largely brought down in one direction, the volume ofthe absorbent composite layer 10 per unit area can be further increased.In addition, as shown in FIG. 13, the top portions of the zigzag patterncan be brought down outwardly in mutually opposing directions to eitherside with a flat area provided in the center.

Such a zigzag structure provides a free and sufficient space thatenables the SAP as used in an absorbent product to easily swell byabsorbing a liquid.

FIG. 14 shows an example of a highly absorbent composite sheet materialas composed according to the present invention. This highly absorbentcomposite sheet material has a structure where a highly absorbentcomposite layer 10 is disposed in bands extending in parallel to eachother at prescribed intervals on either surface of the supporting sheet13 made of an elastic substance, over the highly absorbent compositelayer a corrugated (zigzag) liquid pervious non-woven fabric 14 isdisposed, and in the bottom portions of the zigzag of the non-wovenfabric 14 the non-woven fabric 14 and the supporting sheet 13 are bondedin the bonding areas 15. Thus, each highly absorbent composite layer 10is contained in the channel 16 which is formed between the supportingsheet 13 and the non-woven fabric 14. A highly absorbent composite sheetmaterial of a structure described in the above can be preferably used,for example, in absorbent products such as feminine hygiene products anddiapers, as highly elastic and absorbent sheet material: the highlyabsorbent composite sheet material has a high elasticity in thedirection perpendicular to the longitudinal direction of the highlyabsorbent composite layer 10. In this case, the non-woven fabric 14 isused in contact with the body of a wearer, and body exudates of thewearer are first absorbed by and distributed in the non-woven fabric 14and then absorbed by the highly absorbent composite layer 10. As theabsorbed amount of body exudates increases, the volume of the highlyabsorbent composite layer 10 increases. However, since each band of thehighly absorbent composite layer 10 is contained in the channel 16formed between the supporting sheet 13 and the non-woven fabric 14, thelayer is allowed to swell freely.

FIG. 15 shows a highly absorbent composite sheet material embodying thepresent invention. A liquid impervious sheet designated by referencenumeral 21 in FIG. 15 is liquid impervious and reasonably elastic. Ahighly absorbent composite sheet material 22 is laid on top of theliquid impervious sheet 21. Both of them are bonded with each other atmany bonding areas 23 extending in lines or bands parallel with eachother disposed at prescribed intervals. The bonding areas 23 are formedby thermally fusing, by a conventional method such as heat sealing andhigh frequency bonding, the liquid impervious sheet 21 and the highlyabsorbent composite sheet material 22 with a predetermined width. Inbetween the adjoining bonding aims 23 and 23, the length of the highlyabsorbent composite sheet material 22 is longer than the length of theliquid impervious sheet 21, and, therefore, in between the bonding areas23 and 23, a channel 24 is formed between the highly absorbent compositesheet material 22 and the liquid impervious sheet 21 by the sagging ofthe former. The highly absorbent composite sheet material 22 has astructure, as shown in FIG. 15, where, on either surface of a supportingsheet 13 of spun-bond or dry-laid non-woven fabric made of polyolefinsuch as PP and PE, an absorbent composite layer 10 is supported whichlayer 10 is disposed on the side facing the liquid impervious sheet 21.A sheet product of this structure is outstanding in retaining stably itsown sheet shape even when the sheet product absorbs a large amount ofliquid.

FIGS. 16 to 18 show typically examples of an absorbent sheet having adistribution of patterns as obtained by the above-described means. FIG.16 shows a pattern made by utilizing pulsation, FIG. 17 shows a patternmade by utilizing a branched nozzle, and FIG. 18 shows a pattern made incombination of the two. Examples of a distribution of higher absorbingregions are classified into the following three types: (1) on top of athin absorbent layer distributed on the whole area a partially thicklayer exists; (2) parts of a supporting sheet exposed without anyabsorbent layer, and parts thereof with such absorbent layer existseparately; and (3) in the higher absorbing regions thin and thicklayers coexist. The distribution pattern of high absorbing regions is,for example, a pattern of islands in the sea as shown in FIG. 16, acontinuous band-type pattern with a thin margin as shown in FIG. 17, anda combination of island and band patterns as shown in FIG. 18. Anabsorbent sheet which is coated with a slurry in a distribution ofpatterns is bonded with a supporting sheet stably by press, and thestructure is fixed by removing the liquid component and drying. In doingso, an absorbent sheet yet to be dried which has a distribution ofpatterns, is high in difference in thickness, and contains a lot ofsolvent is likely to adhere on a press roll and to partially peel off.To prevent this, a means of pressing an absorbent sheet covered withtissue or non-woven fabric is available, but an effective means is asfollows: an absorbent sheet is first heat pressed to fit well asupporting sheet and the absorbent layer on the roll is subjected toremoval of the liquid component to fix the structure so that the surfaceis stabilized. Then, if peeling is done only after the surface is thusstabilized, no absorbent sheet is wound on the roll without anycovering.

FIGS. 19(A), (B), (C) and (D) show typically the simplest shape of anabsorbent tube of the present invention. In FIG. 19, reference numeral401 represents a supporting sheet in tube, and 402 represents the SAPcarried by the supporting sheet 401 only on the inner wall. In theabsorbent tube as shown in FIG. 19(A) the supporting sheet 401 is formedhaving a cross-section of a closed ring, and made into tube with theadjoining of both ends bonded with an adhesive agent 403 such as hotmelt type adhesive agent, and carries the SAP 402 nearly uniformly onthe whole surface of the inner wall. In FIG. 19(B), a reinforcing sheet404 is disposed at the adjoining point of both ends of the supportingsheet 401, and both ends of the supporting sheet 401 together with thereinforcing sheet 404 are bonded with the adhesive agent 403. In theabsorbent tube of FIG. 19(C), a flat supporting sheet 401 carrying theSAP 402 on one surface is formed into tube only with one end of thesupporting sheet 401 with the surface carrying the SAP 402 inside, andthe side ends of both of them facing each other in opposition areadjoined as laid on top of each other with an appropriate width ofmargin provided and the portion where they are adjoined is bonded withthe adhesive agent 403. Thus, on one end of the flat absorbent is a tubeformed. In the absorbent tube of FIG. 19 (D), on the side end disposedoutside no SAP 402 exists, and, therefore, the adhesive agent 403 isdirectly applied on the surface of the supporting sheet 401.

As a supporting sheet which can be used in the present invention,substantially all kinds of sheet material composed of fiber web, if theyare liquid pervious and do not have openings large enough for the SAPparticles to pass through, can be used. Examples thereof are melt blownnon-woven fabric, foamed net, extruded fibrillated net, spun-bondnon-woven fabric, carded web non-woven fabric, spun-laced non-wovenfabric, and any combinations of the foregoing materials.

The basic roles of this supporting sheet are to carry the SAP stablyand, at the same time, to prevent the SAP swollen by absorbing a liquidfrom leaking and going out of an absorbent tube. If required, thesupporting sheet can be given other roles by selecting the kinds andshapes of the constituting materials of the supporting sheet. Forexample, by selecting a cellulosic fiber or a blending with a cellulosicfiber as the fiber constituting the supporting sheet, the diffusion ofliquid into carried SAP can be increased. Also, another example ofgiving a different role is that, by using non-woven fabric which is ofhigh elongation, can be elongated with a small force, for the supportingsheet, the sheet itself can be elongated by the absorption and swellingof the SAP. By utilizing these effects, the liquid absorbing capabilityof the SAP can be made to exhibit to the maximum extent, and thediameter of the absorbent tube while no liquid is absorbed can be madesmall which in turn makes small absorbent products using such smallabsorbent tube. In this specification, the term “high elongation” of asubstance means the property that the substance can be elongated orextended easily by a small force applied at least in one direction.

A composite sheet obtained by this method has a structure, for example,as typically shown in FIG. 20(A). In FIG. 20(A), reference numeral 411represents a supporting sheet, 412 represents the SAP, and 413represents the HFFM which bonds the particles of the SAP 412 are bondedwith each other and on the supporting sheet 411. Because this compositesheet can be formed as an extremely thin sheet as thin as 1 mm, it canbe formed in tube as shown in FIG. 20(B), and is suitable as anabsorbent tube of the present invention.

FIG. 21(A) shows a composite sheet of a structure where, unlike anabsorbent tube shown in FIG. 21(B) in which particles of the SAP 412 aredistributed in nearly uniform density, blocks in which a plurality ofthe SAP 412 particles are gathered are formed which blocks are disposedin a suitable distribution. An absorbent tube as shown in FIG. 21(B) canbe formed by folding the composite sheet of FIG. 21(A) in the shape of atube with the surface thereof carrying the SAP 412 particles facinginside. In the structures of FIG. 19 tubes in an O-letter shape areformed by directly bonding the side ends of the supporting sheet witheach other, but in the structures of FIGS. 20(B), 21(B) and 22, tubes ina C-letter shape are formed where the side ends of a supporting sheet asit is made in such tube area bit away from each other. The absorbent ofa tube in such C-letter may dispose a slit between the side ends of asupporting sheet facing either upward or downward. Also, another sheetmaterial 414 may be bonded by means of adhesive 403 to the slit as shownin FIG. 22.

It should be noted that in the above description and in the sketchesthat are shown in the description to follow an absorbent tube is shownin a circle or ellipse or a shape that is somewhat swollen in order tohelp better understand it, but in fact, the absorbent tube before itabsorbs liquid to swell takes a shape that is flat or collapsed.

One or a group of absorbent tubes having a structure described in theabove can be incorporated into a conventional absorbent product as anabsorbent core, but in practice, are advantageously used as linked to asheet comprising an absorbent product. For example, one absorbent tubeor a plurality of absorbent tubes disposed in parallel to each othercomprises or comprise an absorbent core as linked in an absorbing regionof an absorbent product to a liquid pervious inner sheet disposed on theside of the absorbent product in contact with the skin of a wearer or aleakage resistant outer sheet.

FIG. 23 shows a disposable diaper as an absorbent product of the presentinvention having a structure described in the above. In FIG. 23,reference numeral 500 represents the body of an absorbent product. Thisbody 500 is, as shown in FIG. 24, composed of a liquid pervious innersheet 520 and of a liquid impervious outer sheet 530, and in itsabsorbing region three absorbent tubes 501, 502 and 503 disposed inparallel to each other are contained. The absorbent tubes 501, 502 and503 are, in this embodiment of the present invention, linked to a liquidimpervious outer sheet 530 by means of an adhesive 504 such as hot meltadhesive.

FIG. 25 shows a sectional view of the structure of another absorbentproduct of the present invention like FIG. 22. In this example, theinner sheet 520 is linked to the outer sheet 530 on both sides of theabsorbent tube by adhesive 504.

In the example of FIG. 26, the absorbent tube 502 disposed in the centeris wider than the absorbent tubes 501 and 503 disposed on the respectivesides of the absorbent tube 502 so that both side ends of the absorbenttube 502 are laid on the side ends of the absorbent tubes 501 and 503.

In the example of FIG. 27, the relation in widths among the absorbenttubes 501, 502 and 503 is the same as in the example of FIG. 26, but theabsorbent tubes 501 and 503 on the sides are disposed at positionshigher than the absorbent tube 502 disposed in the center and the insideends of the absorbent tubes 501 and 503 are laid on the side ends of theabsorbent tube 502.

The absorbent products of the present invention provided with anabsorbent core of a configuration shown each in FIGS. 24 to 27 exhibit ahigh absorbing property with the absorbing capability of theabove-described absorbent tubes. Particularly, in a configuration asshown in FIGS. 26 and 27 where each absorbent tube is partially laid onan adjoining absorbent tube, because the amount of the SAP per unit areacan be made larger, further higher absorbing property can be expected.For example, a condition where the absorbent tubes 501, 502 and 503 haveabsorbed to swell in a configuration of FIG. 26 is shown in FIG. 28.Also, in examples of FIGS. 24 to 27, each absorbent tube may be linkedto the inner sheet 520, too, so that the absorbent tube may be securedin position.

In the absorbent products of the present invention, an absorbent core tobe disposed in an absorbing region may be comprised only by a pluralityof absorbent materials, as described in the above, but one of theabsorbent tubes may be replaced by another absorbent 506, as shown inFIG. 29.

Alternatively, as shown in FIG. 30, a configuration can be made whereabsorbent tubes of long length and narrow width 507 are disposed inparallel to each other and tapes 508 made of a soft hand sheet such asnon-woven fabric extending along the outer sides of each absorbent tubeare disposed. This tape 508 allows a liquid coming to the absorbingregion to reach the absorbent tube 507 and at the same time improves thetouch existing between the absorbent tube and the skin of a wearer.

The number and the size of the absorbent tubes disposed in the absorbingregion of an absorbent product can be selected depending upon the shape,use and desired absorbing property of the absorbent product, and theselection can easily be made by those skilled in the art.

In the descriptions and drawings made and shown in the above, theabove-mentioned absorbent tubes are shown to have a virtuallyellipsoidal cross-section, but the absorbent tube is normally thinhaving a flat shape before it absorbs a liquid to swell, as shown inFIG. 31. If the absorbent tube is of a single layer, the circumferencelength of the cross-section is constant regardless of the shape of thecross-section. The longer the circumference length is, the larger thearea becomes to be provided to carry the SAP 402, and when the SAP 402swells and increases in volume, the thickness or the height of theabsorbent tube becomes larger. FIGS. 32 to 35 show examples where thesupporting sheet 401 is provided with a gusset for such purpose. In theexample of FIG. 32, a gusset 510 is disposed on the top surface of theabsorbent tube, and in the examples of FIGS. 33 to 35, a gusset 510 isdisposed on each side end of the absorbent tube. Note that in FIG. 34the side ends on which gussets 510 are provided are linked at portionsfacing each other by heat sealing 511, forming a cell 512 asdistinguished from the rest.

In the absorbent tube of the present invention, a supporting sheet canbe composed of any sheet material which is liquid pervious and has somedegree of softness and tear strength. A preferable material is anon-woven fabric 601 as described in the above, and a non-woven fabricof an absorbent composite as shown in FIG. 36 can also be advantageouslyused. This composite non-woven fabric 601 may be made by composing oneor two kinds of staple fiber 602 such as PET and rayon with spunbondnon-woven fabric 601 made of synthetic fiber such as polypropylene bymeans of water jet entanglement. A composite non-woven fabric like thishas a feature where the spunbond non-woven fabric 601 functions as theinner sheet and, as shown in FIG. 37, on the surface of the staple fiberthe SAP 402 particles are securely held so that there is no need tocover the absorbent core with the inner sheet.

FIG. 38 shows an absorbent product of a structure where the absorbentsheet 600 of FIG. 37 is formed into a tube and linked to the outer sheet411 of an absorbent product by means of adhesive 504, and on both sidesleg gathers 603 are provided composed of a liquid impervious sheet.Either side of each leg gather 603 is linked to the outer sheet 411, andthe other side is made to face the end of the other leg gather 603 atsome interval in which interval the center portion of the absorbent tube600 is located.

Other examples of an absorbent sheet of the present invention aredescribed with reference to the accompanying drawings:

FIG. 39 shows a sheet material where on a liquid impervious sheetmaterial 711 made of flexible thermoplastic film many dents 713 areformed having openings 712 in the bottom. An absorbent sheet where thedents 713 are filled with absorbent material is shown in FIGS. 40 and41. The absorbent material is made by fixing the SAP particles 714 onthe inner wall of the dent 713 of the liquid impervious sheet material711 with the HFFM 715.

In general, such a structure is preferable as smaller dents are filledwith finer particles and larger dents are filled with coarser particles.

Also, FIG. 42 shows the steps of making other absorbent sheet of thepresent invention. In the step of FIG. 42(A) a liquid impervious sheetmaterial 721 and a liquid pervious non-woven fabric 722 having a lateralextensibility are laid one each other with a hot melt adhesive layer(not shown) in between, and in the step of FIG. 42(B) many groovedportions 723 extending in parallel to each other are formed by means ofheated grid roll, and at the same time, the liquid impervious sheetmaterial 721 is bonded with the liquid pervious non-woven fabric 722 atthe positions of the grooves with hot melt in between. This compositesheet is, in the step of FIG. 42( c), extended in a directionperpendicular to the longitudinal direction of the grooved portion 723,whereby the liquid impervious sheet material 721 is cut off at thepositions of the grooves 723 to form dents 724. The dent portion is madeup of only the liquid pervious non-woven fabric. Next, in the step ofFIG. 42(D), slurry where the SAP and the HFFM are uniformly dispersed ina dispersion medium of a water miscible organic solvent and water isapplied onto the liquid pervious sheet material 724 and then afterremoving the liquid component and drying, the dents 724 are filled withabsorbent material 725 composed of the SAP and the HFFM. Lastly, in thestep of FIG. 42(E), the topsheet 726 such as non-woven fabric isdisposed on the liquid impervious sheet material 721 and the absorbentmaterial 725 and the liquid impervious sheet material 721 and theabsorbent material 725 are bonded to the topsheet 726 at the position721 where no absorbent exists.

FIG. 43 shows a liquid impervious sheet material where the many dentsformed in the step C of FIG. 42 are circular. FIG. 44 shows a sheetmaterial where the dents 724 in the step D of FIG. 42 are filled withthe absorbent material 725.

In the absorbent sheet as shown in FIG. 42, the non-woven fabric 722constituting the composite sheet together with the liquid impervioussheet material 721 is preferably a non-woven fabric of 10 g/m² to 50g/m² weight such as a non-woven fabric of a hydrophobic synthetic fibersuch as PE, PP and PET and a non-woven fabric of a mixture of asynthetic fiber and a cellulosic fiber such as rayon, Lyocell andcotton.

FIGS. 45 and 46 show configuration where a liquid impervious sheetmaterial 721 is formed in a corrugated sheet and absorbent material 725is disposed and fixed in narrow bands or in bars in the bottoms of dents724 of V-letter shape extending in parallel to each other.

Also, FIG. 47 shows an example where the absorbent material 725 isdisposed in dots, not in bands or bars as shown in FIGS. 45 and 46.

In the structures shown in FIGS. 45 to 47, the liquid impervious sheetmaterial 721 may have or have not openings in the bottoms of the dents724.

In any case, the dents 724 formed on the liquid impervious sheetmaterial may have an inner wall extending perpendicularly to the surfaceof the sheet material, but preferably, should have a funnel-like taperwith the size becoming smaller from top to bottom which allows absorbentmaterial to fill in more easily. The size of dents depends upon the sizeor shape of the absorbent material, but should be at least 0.3 mm,preferably 0.5 mm in the diameter if the dents are circular or, in thewidth of the shorter direction if the dents are long and narrow in theshape of ellipse, rectangle or groove. It is because if the diameter orwidth is too small, it is difficult to hold a sufficient amount ofabsorbent material stably in the dents.

Next, briefly, processes preferably applied in making the absorbentsheet of the present invention are described using the HFFM, the SAP anda short-cut staple fiber component

A process of adding the short-cut staple fiber component is selected,which is optimum depending upon the characteristic or property of theshort-cut staple fiber component, namely in dry state or wet state, thenecessity of fibrillation. FIGS. 48 to 51 show several examples ofrepresentative processes of making the absorbent sheet. From these flowcharts the configuration of each process can easily be understood.

First of all, typical model examples of the composite absorbent of thepresent invention composed of four components of the SAP, the MFC,short-cut staple fibers and a supporting sheet are shown in FIGS. 52 and53. FIG. 52 shows the composite absorbent in a dry state, and FIG. 53shows the composite absorbent of FIG. 52 which has absorbed a liquid andswollen. In FIGS. 52 and 53, reference numeral 111 represents asubstrate, on the surface of which the SAP particles 112, a short-cutstaple fiber component 113, and the HFFM 114 are held. As shown in FIG.52, the SAP particles exist dispersed or with plural particles securelybonded by the MFC when they are in dry state, while groups of the SAPparticles are contained with leeway as covered by the short-cut staplefiber component just like an umbrella.

When body exudates are discharged into the composite absorbent, the SAPabsorbs them to swell. At that time the hydrogen bonds of the MFC arecut off, and the SAP swells more freely but within the network where theSAP is contained so that the SAP is prevented from going out of thenetwork.

FIG. 54 is a structure where, by using a bulky substrate, the effects ofthe network are improved in concert with the effects of the short-cutstaple fiber component. In FIG. 54, reference numeral 111 a represents ahigh density layer of the substrate, 111 b represents a low densitylayer of the substrate, 112 represents the SAP particles, 113 representsshort-cut staple fibers, and 114 represents the HFFM. It is shown thatthe SAP particles are captured with relative leeway among the fibers ofthe low density layer of the substrate 111 b. In the present invention,absorbent layer may be provided all over completely on either surface ofthe supporting sheet, but may also be provided in rows or any desiredpattern. Also, by providing absorbent layer only on either surface ofthe supporting sheet, a composite absorbent having a sufficientabsorbing capacity can be constituted, but in case the supporting sheetis used in such uses as a liquid contacts both sides of the supportingsheet, absorbent layer may be provided on both sides of the supportingsheet.

Methods of evaluating the properties applied in the present inventionare described below:

-   1) Standing sustainability of the swollen SAP in a composite    absorbent when wetted Cut a rectangle of 2 cm×10 cm from the    composite absorbent to make a sample.    {circle around (1)} Standing Sustainability of the SAP

Place two rectangular sample pieces with the SAP side upward atapproximately 2 cm interval on a Petri dish of 12 cm diameter, add 50 mlof 0.9% NaCl (a physiological saline solution) gently and allow to standfor 10 minutes for the SAP to swell. Visually observe the conditionwhere the SAP as swollen come off from the samples into the liquid.

(Judgement Criteria)

⊚ The SAP swells but little SAP is observed to come off.

◯ As the SAP swells, a little SAP is observed to come off.

Δ As the SAP swells, the SAP is observed to come off appreciably.

X As the SAP swells, the SAP is observed to come off very much to pileup in the liquid.

{circle around (2)} Standing Coming Off of the SAP

The procedure is the same including the judgment criteria as in thestanding sustainability test, except that two sample pieces are placedwith the SAP side downward.

{circle around (3)} Vertically Suspending Sustainability of the SAP

Take out the samples from the liquid with a pair of tweezers immediatelyafter the evaluation in the above-described standing sustainabilitytest, hold one end of the longitudinal direction with a clip tovertically suspend, and virtually judge the condition of the swollen SAPcoming off from the supporting sheet.

(Judgement Criteria)

⊚ Little swollen SAP is observed to come off.

◯ A little SAP as swollen on the surface is observed to come off.

Δ Of swollen SAP, a part of the SAP on the surface is observed to comeoff, but the SAP in direct contact with the supporting sheet is notobserved to come off.

X A majority of swollen SAP is observed to come off.

2) Dispersion of an Absorbed Liquid by a Composite Absorbent

Cut a circle of 5 cm diameter from the composite absorbent to make asample.

{circle around (1)} Absorbing Time of Dropped Liquid (Seconds)

Place the sample on a Petri dish of 12 cm diameter with the SAP sideupward, drop 1 ml of 0.9% NaCl (a physiological saline solution) with aburette in the center of the sample taking approximately one second, andmeasure the time (seconds) until the dropped liquid is absorbed.

{circle around (2)} Dispersing Time (Seconds)

Put 100 ml of 0.9% NaCl (a physiological saline solution) in a Petridish of 12 cm diameter, float the sample with the SAP side upward withthe side of the supporting sheet in contact with the liquid, and measurethe time until the liquid disperses on the whole surface of the sampleand the applied SAP finishes swelling on the whole surface.

3) Thickness of Supporting Sheet (mm)

Cut a circle of 5 cm diameter from the supporting sheet to make asample. Measure using a thickness gauge of Daiei Chemical PrecisionInstruments Mgt. Co., Ltd. with the area of the probe of 15 cm² (43.7 mmdiameter) and the measuring pressure of 3 g/cm².

4) Apparent Density of Supporting Sheet (g/cm³)

Calculate from the weight (g/cm²) and the thickness of the supportingsheet by the following formula:Apparent density(g/cm³)=[weight(g/m²)/10⁴]×[10/thickness(mm)]

Other composite absorbent sheet embodying the present invention aredescribed where an absorbent sheet is provided with a liquid pervioussupporting sheet and an absorbent layer containing the SAP particlesbonded to either surface of the liquid pervious supporting sheet withthe absorbent layer forming a plurality of high absorbing regions havinghigher absorbing capability than the other regions as distributed in adesired pattern on the surface of the liquid pervious supporting sheet.

FIG. 55 typically shows a plurality of high absorbing regions havinghigher absorbing capability of the absorbent layer and low absorbingregions having lower absorbing capability on the supporting sheetembodying the present invention; on the drawing the white colored partsshow high absorbing regions 210 and the black colored parts show lowabsorbing regions 220.

FIG. 56 is a longitudinal cross-sectional view of a part of theabsorbent sheet shown in FIG. 55. Reference numeral 203 represents asupporting sheet made of material such as non-woven fabric having anappropriate liquid perviousness, and on either surface of thissupporting sheet 203 absorbent layers 200 are provided forming regionsof higher absorbing capability 210 and regions of lower absorbingcapability 220.

The absorbent layers 200 are composed of the SAP particles 201 and theHFFM 202 existing around each particle 201, and the HFFM 202 bonds theSAP particles 201 together and is bonded to the surface of thesupporting sheet 203 to function as a means of transferring a liquid tobe absorbed to each particle.

In the examples shown in FIGS. 55 and 56, the difference in absorbingcapability between the high absorbing region 210 and the low absorbingregion 220 of the absorbent layer is realized by the difference in thethickness of the absorbent layer. This thickness is representedapparently by the configuration of the layer of the absorbent polymer,and as shown in FIG. 56, the thinner layer is in one layer, and thethicker layer is in two or more layers.

An example of non-woven fabric having preferable properties as materialof the absorbent sheet of the present invention is, as previouslyproposed in Japanese Patent Examined Publication No. HEI 9-59862 of thepresent applicant, non-woven fabric where spunbond having a bi-componentstructure is used, stretched and heat set by a method shown in FIG. 57to provide a cross-sectional structure as shown in FIG. 58. Thisnon-woven fabric has a property of being more likely to elongate muchonly in one direction. In FIG. 58, the preferable range of H is 0.2 mmto 2 mm, and the preferable range of L is 1 mm to 5 mm.

Another example of non-woven fabric is, as previously proposed by thepresent applicant in his Japanese Patent Application No HEI 8-345410,non-woven fabric where a highly elastic net and a fiber web arepartially laminated. This laminated non-woven fabric has a structure, asshown in FIGS. 59 and 60, where on both surfaces of a net 407 wherelongitudinal elastic string 405 and lateral elastic string 406 areintersected with each other and bonded at points of intersection,identical or different webs 408 and 409 are laminated, and the net andthe web are bonded along bonding lines 410 arranged in parallel to eachother so that the laminated non-woven fabric has a property of beinglikely to elongate much only in one direction perpendicular to thebonding lines 410.

The SAP can be beforehand carried by a supporting member previouslyformed in the shape of a sheet, but can also be introduced into asupporting sheet when the supporting sheet is manufactured by practisingthe present invention. An absorbent composite can be obtained, forexample, by making a carded web of easy-to-melt synthetic staple fiberand fibrous SAP, by, after laminating a pulp, the SAP and easy-to-meltstaple fibers by an air-laid method, heat treating to fix the laminatedcomposite, or by, after impregnating a non-woven web with acrylic acidmonomer, polymerizing and cross-linking such impregnated non-woven web.The surface of the carried SAP may be exposed or may be covered bytissue or the like.

Next, with reference to the accompanying drawings, an apparatus suitablefor making the absorbent composite of the present invention is describedbelow:

In FIG. 61, reference numeral 31 represents a tank for storingion-exchanged water, 32 represents a tank for storing the HFFM stocksolution, 33 represents a tank for storing acetone, and 34 represents atank for storing the SAP. The HFFM water dispersed stock solution takenfrom the tank 32 is introduced into a mixing unit 35 provided with astirrer, diluted in the mixing unit 35 with water taken from the tank31, and, then, pumped into a second mixing unit provided with a stirrer.Into the mixing unit 36, acetone taken from the tank 33 is introduced,and this mixture is pumped into a third mixing unit 37 provided with astirrer. Into the mixing unit 37 the SAP particles are introduced fromthe tank 34, and in this mixing unit the HFFM, the organic solvent,water and the SAP are mixed to form their mixture.

On the other hand, an appropriate supporting sheet 13 of such materialas non-woven fabric is unrolled from a roll 38 and then introduced to aforming area 40. The forming area is provided with a belt conveyor 41and a nozzle 42 located disposed over the belt of the belt conveyor. Themixed dispersion liquid from the mixing unit 37 is pumped to this nozzle42. While the supporting sheet 13 is being conveyed by the belt conveyor41 at a prescribed speed, the mixture dispersion liquid is sprayed fromthe nozzle 42 onto the supporting sheet 13. The nozzle 42 may be ofvarious configurations depending upon the pattern of absorbent compositelayers formed on the supporting sheet 13.

The forming area 40 is further provided with a roll press 43 composed ofa pair of rollers. The supporting sheet coated with the mixturedispersion liquid is pressed by the roll press 43 so that the solventcontained in the dispersion medium is squeezed and the solvent asseparated is pumped to the second mixing unit 36.

The supporting sheet 13 after coming out of the forming area is sent toa drying area 50. To the drying area 50 hot air is supplied in whicharea a pair of porous rolls 51 and 52 are provided. The supporting sheet13 and the mixture dispersion liquid sprayed on the sheet are driedwhile they are being conveyed along the peripheries of the porous rolls51 and 52.

The supporting sheet after coming out of the drying area is compressedin a compressing area 60 consisting of a pair of press rolls 61 and 62,and thus, a product where absorbent composite layers are formed on thesupporting sheet 13 is obtained.

FIG. 62 shows a system wherein an apparatus for making the HFFM fromacetyl cellulose is combined with the apparatus shown in FIG. 61. Inthis system acetate dope is stored in a tank 31 a, a coagulation liquidis stored in a tank 32 a and acetone is stored in a tank 33 a. Theacetate dope and the coagulation liquid from the tanks 31 a and 32 a aresent to an aspirator type fibrillating unit, where fibrillation iscarried out. The fibrils are refined in a mixing unit 35 a to obtainfiner fibrils, namely the HFFM in slurry. The HFFM are then mixed in asecond mixing unit 36 a with acetone from the tank 33 a, and again mixedwith the SAP in another mixing unit (not shown). The subsequent stepsare the same as those of the process of FIG. 61.

FIG. 63 shows an example of another apparatus for applying a mixturedispersion liquid onto the supporting sheet 13 in the forming area 40 ofFIG. 61. In FIG. 63, reference numeral 44 represents a top-opened tankfor storing a mixture dispersion liquid, and in the tank 44 a dippingroll 45 is disposed which is rotatable with a horizontal shaft in thecenter with a part of the periphery being dipped in the mixturedispersion liquid. Also, a pair of rolls 46 and 47 are provided whichare rotatable with a shaft in the center in parallel, respectively, tothe dipping rolls 45. The roll 46 is contacted with the periphery of thedipping roll 45 with pressure, and, as, for example, shown in FIG. 64,has many ring shaped grooves on the periphery. Through the nip betweenthe roll 46 and the other roll 47 which has a flat surface, thesupporting sheet which is to be coated with the mixture dispersionliquid is made to pass. The mixture dispersion liquid stored in the tank44 deposits by its own viscosity on the periphery of the dipping roll 45rotating in the tank, and is transferred onto the supporting sheet viathe groove roll 46. Thus, as shown in FIG. 65, mixture dispersion liquidlayers 48 in many bands arranged in parallel to each other are formed onthe surface of the supporting sheet. The grooved pattern formed on theroll 46 can be freely designed, and the mixture dispersion liquid can beapplied onto the supporting sheet in a pattern corresponding to thepattern on the roll 46.

The features and properties of an absorbent product in which the highlyabsorbent composite is incorporated are described briefly below:

When the highly absorbent composite is used in an absorbent product,firstly, the product is extremely thin and compact before worn and Whileworn before it absorbs a liquid, so that the SAP particles are heldsecurely and stably and therefore, if it is folded or bent, the SAPparticles do not move or come off. The structure of the product does notbreak down.

Secondly, when a liquid is absorbed by the absorbent product, althoughit is of a structure of pulpless with 90% or more of the SAP, theproduct absorbs the liquid very quickly without blocking thanks to thehydrophilicity and physical forms of the HFFM.

Thirdly, after a liquid is absorbed, swollen polymer particles are heldstill securely by the network of the HFFM and are thus prevented fromcoming off.

The fourth feature of the absorbent product relates to a characteristicwhen it is disposed of. The absorbent of the present invention when itis in contact with excessive water remains stable as it is, but, ifshearing force is applied, it immediately is dissociated. The absorbentis suitable for making a flushable. In addition, since the cellulosicHFFM is extremely high in cellulase enzyme activity, the structure ofsuch HFFM if buried in the land is dissociated in a short period oftime. Further, if any biodegradable aminoacetic type absorbent polymeror the like is combined to make the SAP, an ideal nature-friendlyabsorbent can be designed.

The configuration of an example of an apparatus for making the absorbentsheet as shown in FIGS. 55 and 56 is described with reference to FIG. 66below. In FIG. 66, reference numeral 311 represents a slurry supplyingpipe by means of which a slurry dispersion liquid containing the HFFMand the SAP is supplied, and to the slurry supplying pipe 311 aplurality of pipes 313 each on the top end of which a nozzle 312 isprovided is connected. Each pipe 313 is provided with a pump 314 as atransferring means of sucking the slurry dispersion liquid from theslurry supplying pipe 311 and discharging the liquid from the nozzle312. The pump is driven by a motor 315 which is used in common.

On the other hand, it is so designed that the liquid pervious supportingsheet 203 which is to be coated with the slurry dispersion liquiddischarged from the nozzle 312 is conveyed at a constant speed in adirection indicated by an arrow in the drawing. Each pump 314 is capableof supplying the slurry dispersion liquid at a periodically varyingpressure to the nozzle 312, and as a result, on the liquid pervioussupporting sheet 203, bands 316 of slurry dispersion liquid of a numbercorresponding to the number of the nozzles 312 are formed and each band316 can be made different in the thickness of the absorbent layer andhas a indefinite margin.

A means of forming a distribution of patterns is that, at the step ofcoating the surface of the liquid pervious supporting sheet with thedispersion liquid supplied in a constant flow, a nozzle is used having astructure or function of imparting an appropriate pattern to thethickness and/or width of the coated layers.

A nozzle of this function may be ones shown in FIGS. 67 and 68. Thenozzle 312 shown in FIG. 67 has a structure that two slits having aprescribed length each are formed from the tip portion of the tubeshaped body 320 and the tip portion is divided into two tips 321 and322, and, as a result, a discharging outlet is formed on each of thetips 321 and 322.

In addition, the nozzle 312 shown in FIG. 68 has a structure that fourslits having a prescribed length each are formed from the tip portion ofthe tube shaped body 320 and the tip portion is thus divided into fourportions 323 to 326. In this case, on each tip of the four portions 323to 326 a discharging outlet is formed.

Examples of other structures of the nozzle are shown in FIGS. 69 to 71.The nozzle 312 of FIG. 69 has a structure in which on the tip of thetube 331 having rigidity or some flexibility a tongue portion 332 isformed in an integrated way. Also, the nozzle 312 of FIG. 70 has astructure in which on the tip of the tube 331 a separately preparedtongue portion having rigidity or some flexibility is mounted. Further,the nozzle 312 of FIG. 71 has a structure in which on the tip of thetube 331 a separately prepared flexible tongue portion 334 and areinforcing member 335 on the outside of the tongue portion are mounted.

In the cases of the nozzles shown in FIGS. 69 to 71, a dischargingoutlet on the opening on the tip of the body 331 and an dischargingoutlet on the tip of each tongue portion 332 to 334 are formed so thateach nozzle is provided with a plurality of discharging outlets.

These nozzles 312 are disposed at right angles to the liquid pervioussupporting sheet 203 to be coated with the slurry dispersion liquid asshown in FIG. 72 or inclined by some degrees q to the liquid pervioussupporting sheet to be coated with the slurry dispersion liquid as shownin FIG. 73. When the slurry dispersion liquid is discharged from thenozzle of this disposition, the dispersion liquid is discharged in adirection of lower resistance depending upon the discharging pressure sothat coating is conducted in a pattern having indefinite margins.

The reason why the above-described operation is conducted with relativeease is because the slurry containing the SAP and the HFFM has astructural viscosity (thixotropic flow). The property of the slurry maybe contributing to the easy operation of the coating that the slurry isdischarged from the nozzle keeping a high liquidity while it has adischarging flow velocity, but after discharged it loses the liquidityand solidifies.

As a result of this, a plurality of high absorbing regions in bandsvaried in thickness and having indefinite margins are formed on thesurface of the liquid pervious supporting sheet.

Another means of forming a distributed pattern of absorbent layers onthe supporting sheet is to give pulsation effects by incorporating apulsation generating area in either of or both of the nozzle portionincluding a header and the feeding mechanism of the supporting sheet. Bythis means absorbent layers which are periodically varied in thicknessand width can be formed. In the above, the methods of utilizing thepulsation of a pump, utilizing a special type of a nozzle, and vibratingan apparatus to give pulsating effects to the dispersion slurry as themeans of forming a distribution of patterns are described. To becombined with either of the methods there is a means of making such SAPas is different in particle size or shape or gives a large difference inabsorbing speed co-exist in the dispersion slurry. In this case, withthe uniform dispersion and the stable discharging from the nozzle takeninto consideration, it is preferable to disperse such SAP as is oflarger particle size or of different shape in a dispersion system ofsuch SAP as is of relatively fine particle size.

Now, the purpose of forming a distribution of patterns like this is thatwhile, having different distributions of concentrations (higher andlower concentrations), of densities (higher and lower densities), and ofthickness (thicker and thinner) and at the same time increasing thesurface area of lower concentration portions, rapid absorbing anddiffusion are obtained by utilizing lower concentration portions ornon-absorbing portions and time requiring but stable absorbing isrealized by utilizing thicker concentration portions so that anabsorbent suitable for absorbing as many times as possible utilizing astructure of as many phases as possible can be designed. On the otherhand, by imparting this structure sufficient flexibility can be impartedto the whole of an absorbent sheet to fit well the body of a wearer. Inother words the portion which is coated thick with absorbent layer hasrigidity and is hard to be bent while the portion which is little or notcoated with absorbent layer is very easy to be bent with the property ofthe supporting sheet itself maintained.

This method is extremely effective from the commercial viewpoint. FIGS.74 and 75 show examples a process of making an absorbent sheet having aplurality of high absorbing regions having high absorbing capabilitydistributed in a pattern according to the present invention.

A coating apparatus shown in FIG. 74 is composed as follows: a suctionroll 341 and a heat press roll 342 supported with a shaft and arrangedin parallel to each other are provided and a liquid pervious supportingsheet 203 is guided via guide roll 343 to the suction roll 341 and atthe position where the liquid pervious supporting sheet 203 is rotatedapproximately one fourth of the periphery of the suction roll 341, theliquid pervious supporting sheet 203 comes in contact with the heatpress roll 342, and then while in contact with the heat-press roll 342the liquid pervious supporting sheet 203 is rotated approximately onehalf of the periphery of the heat press roll 342, and finally is guidedvia a guide roll 344 to a dryer (not shown).

A suction area 345 is provided in the suction roll 341, which area formsa region for sucking the liquid pervious supporting sheet 203 conveyedin contact with the periphery of the suction roll 341. A nozzle 312 isdisposed at a position where the nozzle 312 can to discharge a slurrydispersion liquid onto the surface of the liquid pervious supportingsheet 203 in this suction area, and forms layers in a desired pattern onthe liquid pervious supporting sheet 203. Reduced pressure generated inthe suction area makes the slurry dispersion liquid adhere to thesurface of the liquid pervious supporting sheet 203 and at the same timesucks an excess of the solvent contained in the slurry dispersion liquidtogether with surrounding air. The sucked liquid is guided via a pipe346 to a strainer 347 where the liquid is separated into solvent andgas. The solvent thus separated is taken out via a pipe 349 for recycleto form a slurry dispersion liquid, and the gas is discharged outsidefrom a pipe 348 via a vacuum pump (not shown).

The liquid pervious supporting sheet 203 is then conveyed while incontact with the heat press roll 342, in the process of which slurrydispersion liquid as heated is adhered to the liquid pervious supportingsheet 203, and the obtained absorbent sheet is then guided via the guideroll 344 to the dryer where the absorbent sheet is dried finally.

A coating apparatus shown in FIG. 75 is only different from the coatingapparatus of FIG. 74 in that in addition to the suction area 345disposed facing the nozzle 312, a second suction area 350 is provided asdisposed in the nip with a heat press roll 342. In the second suctionarea 350, the solvent is further strongly sucked and separated from theslurry dispersion liquid while the slurry dispersion liquid is pressedbetween a suction roll 341 and a heat press roll 342.

A coating apparatus shown in FIG. 76 is different only in that a nozzle312 is designed to apply a slurry dispersion liquid not over a suctionroll 341 but on the periphery of a supporting roll 351 provided beforethe suction roll 341.

Slurry to be obtained by dispersing the SAP and the MFC in a dispersionmedium of water/organic solvent, when the slurry is discharged from anozzle and applied to a supporting sheet to form an absorbent sheet, islikely to be separated into two phases depending upon the conditions ofthe dispersion medium, solids may settle. Therefore, the solids in theslurry may settle in the transportation in a configuration of theapparatus where, as shown in FIG. 61, the slurry is guided to a nozzlevia a dispersion tank, a slurry pump, a pipe, and a header (supplyingtank). In such case, it is preferable to directly connect a dischargingnozzle to each slurry pump and to apply the slurry from this dischargingnozzle. FIG. 90 shows an example of this structure: slurry is applied inmany bands extending in parallel at intervals.

In the configuration illustrated in FIG. 90, slurry is applied in manybands extending in parallel at intervals on a supporting sheet as shownin FIG. 91. In applying the slurry on the whole surface of thesupporting sheet, two pairs of a plurality of slurry pumps provided witha plurality of discharging outlets may be arranged in front and in rearin the direction of running of the supporting sheet so that thedischarging nozzles in rear are disposed in between the dischargingnozzles in front.

EXAMPLES

The examples of practicing the present invention are describedhereunder.

Example 1

Preparing the HFFM Dispersion Liquids

Ethyl alcohol and ion-exchanged water were added to a dispersion liquidof the S-MFC (made by Tokushu Paper Mfg. Co., Ltd.) in gel state of 3.0%water dispersion as a stock liquid, to make three kinds of microfibrildispersion liquid where the ratio of ethyl alcohol/water was 70/30 andthe concentrations of the S-MFC were 0.25%, 0.5% and 1%, respectively.

Preparing the HFFM/SAP Coexistent Dispersion Liquids

10 grams of the SAP (made by Sanyo Chemical Industries, Ltd. under thetrademark “IM-6700”) passed by 60 to 100 mesh was added to 50 cc of eachof the above-mentioned three kinds of the HFFM dispersion liquid toprepare The HFFM/SAP dispersion slurry.

The prepared dispersion slurry is described as follows:

TABLE 2 Ethyl alcohol/ Concentration Experiment No. water of S-MFC (%)S-MFC/SAP × 100 (%) No. 1 70/30 0.2 0.1 No. 2 70/30 0.5 2.5 No. 3 70/301.0 5.0Forming the HFFM/SAP Composite Sheet Material

Each of the dispersion liquids while stirred was subjected to removingthe liquid component under a pressure reduced by an aspirator, and thendried at 5° C. under reduced pressure while spread on a PP non-wovenfabric.

The composite after dried was formed in soybean shaped lumps. Thecomposite in lumps as wrapped in a fine mesh shirting was crushed with awood hammer, and passed by a 40 to 60 mesh to run absorbing tests.

TABLE 3 Experiment No. Crushed state No. 1 Relatively easily crushed No.2 Hardened and hard to be crushed No. 3 Hardened in pebble-like lumpsand stickly, and extremely hard to be crushed

The highly absorbent composite crushed into powder had, observed by amicroscope, its surface covered with the HFFM as shown in FIGS. 7( a)and 7(b).

Evaluating Absorbency

The water absorbing speed, gel block state, absorbed amount of water,and retained amount of water of the above-described SAP (both passing by60 to 100 mesh and 40 to 60 mesh) were measured. For the absorbingspeed, an initial absorbing time (sec.) required for absorbing 20 cc ofwater was measured. For the absorbed amount of water and the retainedamount of water, the SAP, after dipped in an excessive amount ofphysiological saline solution, was measured in accordance with JISK-7223. The measured results are as shown in Table 4:

TABLE 4 Blank No. 1 No. 2 No. 3 Absorbed amount of 45 47 44 46physiological saline solution (g/g) Retailed amount of 35 34 34 36physiological saline solution (g/g) Absorbing speed of 15  5 10 30physiological saline (Unswollen (Unswollen lump solution (sec.) lumpgenerated) partly generated)

As clearly shown in the above-tabulated results of measurements, theabsorbency and the water retention were little affected by adding theS-MFC. On the other hand, as the concentration of the S-MFC wasincreased from No. 1 to No. 3, the bonding strength of the SAP wasincreased, but the SAP became harder to handle because it was hardened.Moreover, since the concentration increased, the absorbing speed waslowered. Therefore, in such applications as such properties (absorbingspeed and the like) are important, the percentage of the HFFM to beadded to the SAP should be preferably 5% or lower.

Example 2 Concentration of the HFFM and the Properties of a CompositeSheet Material

Preparing the HFFM Dispersion Liquid

Preparing a Bacteria Cellulose (BC) Stock Solution

BC (made by B.P.R.) where the concentration of solids was 30% wasstirred and dissolved in ion-exchanged water by a mixer forapproximately 2 hours to prepare a stock solution where theconcentration of solids was 1.2%.

Preparing Ethyl Alcohol/Water Dispersion Liquids of BC

Ethyl alcohol and water were added to a prescribed amount of the stocksolution to prepare BC dispersion liquids of 0.02% to 0.80% BC.

Preparing the HFFM/SAP Coexistent Dispersion Liquid

5 grams of the SAP (made by Sanyo Chemical Industries, Ltd.) was addedto 50 cc of each of the dispersion liquids of 0.02% to 0.8% BC toprepare BC/SAP dispersion liquids. In case the concentration of the BCwas lower in the dispersion liquid, the SAP settled, but as theconcentration of the BC became higher, it became stabilized. By stirringwith a stirrer, the systems were kept stabilized to match the conditionsof the systems as desired.

The descriptions of thus obtained BC/SAP coexistent dispersion liquidsare as follows:

TABLE 5 Experiment Ethyl Concentration BC/SAP × No. alcohol/water of BC(%) 100 (%) No. 11 70/30 0.02 0.2 No. 12 70/30 0.05 0.5 No. 13 70/300.10 1.0 No. 14 70/30 0.20 2.0 No. 15 70/30 0.40 4.0 No. 16 70/30 0.808.0 Blank 70/30 0   0  Forming the HFFM/SAP Composite Sheet Material

A filter paper and a substrate non-woven fabric (made by FutamuraChemical Co., Ltd. under the trademark “TCF 403”, of an apparentspecific density of 0.07 gram/cm³) were laid on a Buchner funnel of a 11cm inner diameter as connected to a pressure reducing apparatus, and 20cc of the sticky dispersion liquid was poured quickly onto the substratenon-woven fabric. The non-woven fabric was subjected to removal of theliquid component under reduced pressure and dried in hot air to form acomposite sheet.

Comparison of the Properties of Composite Sheet Materials

The properties of the composite sheet materials where the concentrationsof the BC were different were evaluated and compared, which results areshown in Table 6. The experimental results show that, as the addedamount of the BC was increased, the surface strength of the compositesheet materials was increased very much while the rigidity of the sheetswas increased on the other hand. Therefore, it is necessary to properlyselect the a added amount of the BC according to the applications.

TABLE 6 Experiment No. No. 11 No. 12 No. 13 No. 14 No. 15 No. 16 BlankBC/SAP ratio (%) 0.2 0.5 1.0 2.0 4.0 8.0 0 Thickness (mm) 0.60 0.60 0.550.56 0.58 0.57 0.55 Weight (g/cm²) 126 131 128 126 135 130 135 DepositedSAP + BC 88 93 90 88 97 92 97 g/cm²) Apparent specific 0.22 0.24 0.240.24 0.25 0.24 0.28 gravity (g/cm³) Rigidity (mm) 85 78 68 40 25 15 85180 degree peeling test Grade 2 Grade 3 Grade 3 Grade 4 Grade 5 Grade 5Grade 1 using cellophane adhesive tapeThe evaluation methods for evaluation items are described below:

Thickness (mm): Measured by a thickness gauge (JIS) in the same way asdescribed in the above.

Weight (g): Measured together with the substrate of 110 mm diameter byan electronic Roberval balance.

Deposited SAP and BC (g/m²): Calculated by deducting the substratenon-woven fabric from the above weight and expressed in grams per squaremeter.

Apparent specific density (g/cm³): Calculated from the thickness and theweight of the substrate non-woven fabric and the weight of the depositedSAP and BC.

Rigidity (mm): A sample of 110 mm×20 mm was measured by a method asshown in FIGS. 77 and 78. One end of the sample S was placed at the edgeof a stainless steel measure M at right angle, and the scale of themeasure was read at the position where the sample sagged (a mm).

Evaluating the Bonding Stability of the SAP (180 Degree Peeling TestUsing Cellophane Adhesive Tape)

A cellophane adhesive tape (made by Nichiban Co., Ltd. under trademark“CELLOTAPE”) of 15 mm width was adhered on the sample in an adhered areaof 15 mm×10 mm, and the adhered area was pressed lightly with a flannelcloth, and a load of 1 kg/cm² was applied for 10 minutes. After the loadwas removed, the cellophane adhesive tape was peeled off by hand fromthe sample in a 180 degree peeling condition. By measuring the adheredarea (%) of the SAP adhered on the cellophane tape, the bonding strengthof the HFFM was judged by such adhered area of the SAP. The judgementcriteria are shown in FIG. 79.

Evaluating Absorbed Amounts of Water and Retained Amounts of Water byComposite Samples

The composite samples were dipped in a sufficient amount ofphysiological saline solution for 30 minutes and then the absorbedamounts of water and the retained amounts of water were measured by JISK-7223. The measurements were converted into the SAP contents. Theresults are shown in Table 7 below:

TABLE 7 Absorbed amount Retained amount Experiment No. of water (times)of water (times) Used SAP samples 45 37 (Blank) No. 12 44 36 No. 13 4638 No. 14 48 36

Example 3 Continuous Coating Experiments

A highly absorbent composite was made by using an apparatus as shown inFIG. 61 provided with a coating unit as shown in FIG. 63, using thefollowing materials:

(1) Microfibril: S-MFC (made by Tokushu Paper Mfg. Co., Ltd.)

(2) SAP: 1M-4000 (made by Hoechst-Celanese Co.)

(3) Suspension medium: Acetone/water system

Component % by weight S-MFC  0.4 SAP 30.0 Acetone 48.8 Water 20.8(5) Supporting sheet: A two-layered through-air thermal bond webnon-woven fabric (40 g/cm², apparent specific density of 0.06) havingthe following composition was used:

Upper layer: Mixed web of rayon (4 denier×45 mm length (70%)) and PE/PET(2 denier×45 mm length (30%)), approximately 25 g/cm²

Lower layer: Single web of PE/PET bicomponent fiber (2 denier×45 mmlength), approximately 15 g/cm².

A mixture dispersion liquid of the composition in (4) above wascontinuously applied in approximately 10 mm width at an interval of 5 mmwidth onto the surface of the supporting sheet 13 while the sheet wasconveyed at a speed of 10 m/min. Afterwards, the solvent was removedfrom the supporting sheet as compressed by a roll, and then dried in hotair.

The obtained highly absorbent composite sheet had the followingcharacteristics:

Weight 195 g/cm² Amount of SAP 150 g/m² Rigidity Longitudinal: 20 mmLateral 75 mm Surface strength class 5 (180 degree peeling test)

The retained amount of water in the absorbent was measured by JISK-7223. As a result, the SAP retained water at the rate of 40.2 grams ofwater per 1 gram of the SAP, which was nearly equivalent to the level ofthe “blank”.

Example 4

A commercially available ultra thin disposable diaper was used as the“blank”. A sample was prepared by removing absorbent componentsincluding tissue from one of such disposable diapers and by, for suchabsorbent components, incorporating an absorbent composed of a highlyabsorbent composite of the present invention.

The absorbent incorporated in the sample was prepared in the followingprocedure: first, a composite sheet as obtained in Example 3 above wascut in a shape and dimensions as shown in FIG. 80. On the other hand, apulp mat provided with tissue of approximately 90 g/cm² was prepared.Water drops were sprayed onto the composite sheet by a hand spray for adomestic use iron to make the weight of the sheet 2 to 3 g/cm². The cutabsorbent was laid on the sheet, and pressed under pressure by an ironat a temperature of 140 to 150° C.

Five pieces of the sample were prepared. For each sample piece, theabsorbed amount of water, retained amount of water and rewet weremeasured. The absorbed amount of water and the retained amount of waterwere measured by HS K-7223. The rewet was measured as follows: 120 cc ofphysiological saline solution was poured onto a sample three times at 5minute interval, and the rewet was measured for each of the three timesunder the pressure of 12.5 kg per absorbent area.

The above-described test results are tabulated in the following table.The measurements are shown in the average of the five sample pieces.

TABLE 8 Sample of the Blank present invention Configuration of absorbentMeasurement item Thickness (mm) 3.2 1.5 Weight of whole absorbent (g/p)26.0 17.5 Fluff pulp (g/p) 11.8 6.1 Tissue (g/p) 4.0 0.5 SAP (g/p) 10.210.9 Property of absorbent Measurement item Absorbed amount of water(g/p) 665 557 Retained amount of water (g/p) 420 42.5 Re-wet (g) Firstre-wet (120 cc) 0.6 0.4 Second re-wet (240 cc) 0.8 0.9 Third re-wet (360cc) 3.9 2.2

From Table 8 it is shown that a sample where an absorbent composed of ahighly absorbent composite of the present invention, which isapproximately 70% in weight and one half in thickness of a commerciallyavailable disposable diaper, has equivalent or superior absorbingproperties compared with the latter.

Example 5

1) Preparing a SAP Slurry

To a dispersion liquid of 2.15% water of the S-MFC (made by TokushuPaper Mfg. Co., Ltd. under trademark “Super Microfibril Cellulose”),required amounts of water and ethanol were added to prepare aethanol/water dispersion liquid (ethanol/water ratio being 60/40) wherethe concentration of MFC was 0.86% by weight.

To this dispersion liquid a short-cut staple fiber component composed oflow melting point polyester/PET bicomponent fiber of 1.5 denier and 2 mmfiber length was added in an amount equivalent to the amount of theS-MFC, and dispersed with a mixer. Then, as it was stirred in a stirrerwith a propeller, a required amount of the SAP (made by MitsubishiChemical Co., Ltd. under the trademark “Aquapearl US-40”) was added tomake a three component slurry composed of 30% by weight SAP, 0.6% byweight MFC and 0.6% by weight short-cut staple fiber component.

2) Preparing a Supporting Sheet

A two-layered spun-lace non-woven fabric where a first layer wascomposed of fine denier rayon fiber of 1.25 denier and 51 mm length anda second layer was composed of coarse denier PET fiber of 6 denier and51 mm length was prepared. The weight of this non-woven fabric was 30g/m², with an apparent specific density of 0.025 g/cm³, with the firstlater of higher density and the second layer of lower density.

3) Preparing Composite Absorbent

The three-component slurry was applied onto the second layer of thesupporting sheet with a coater in an amount to make the deposited amountof the SAP 150 g/m². Then, immediately after it was sucked and theliquid component was removed, it was hot pressed for a few minutes at180° C. The supporting sheet was then dried in hot air to make acomposite absorbent (I).

Also, the composite absorbent (I) was then dried in hot air again at150° C. to make a composite absorbent (II).

The structure of the absorbent composites (I) and (II) was observed by amicroscope. As shown in a sketch of FIG. 54, it was confirmed that on asecond layer 111 b of a supporting sheet composed of a first layer 111 aand the bulky second layer 111 b and in the space, the SAP particles 112were piled and the short-cut staple fiber component existed as entangledwith the SAP particles and covering the SAP particles like an umbrella,and, on the surfaces of the SAP particles and of the short-cut staplefiber component, the MFC 114 was deposited.

Comparative Example 1

In Example 1, a procedure applied in making the composite absorbent (II)was applied to make a composite absorbent (ii) except that no short-cutstaple fiber component was added.

<Evaluating the Composite Absorbents>

With the three kinds of absorbent composites obtained in Example 1 andComparative Example 1 used, the sustainability of the swollen SAP andthe diffusion of absorbed liquid by the swollen SAP when wet were testedby the above-described testing methods. The test results are summarizedin Table 9 below:

TABLE 9 Dispersion of Sustainability of swollen SAP absorbed liquidStanding Time till Composite sustain- Standing Vertically Absorbingdispersion absorbent ability falling-off suspended time (sec.) finished(sec.) (I) ⊚ ⊚~◯ ⊚~◯ 3~4 40~50 (II) ⊚ ⊚ ⊚ 3~5 50~60 (ii) Δ Δ Δ 3~4 40~50From the test results tabulated in the above, the following judgementscan be made:{circle around (1)} Sustainability of the Swollen SAP

The composite absorbent (I) showed a good retention of the swollen SAP,which was made with a bicomponent short-cut staple fiber containing aneasy-to-melt component incorporated.

The composite absorbent (II) which was heat treated adequately showed anoutstanding sustainability in a particularly rigorous test of avertically suspended sustainability.

However, the composite absorbent (ii) in Comparative Example 1 where noshort-cut staple fiber component was incorporated showed substantiallylower sustainability of the swollen SAP than the absorbent composites(I) and (II) in Example 1.

This was probably because, by incorporating short-cut staple fiberscontaining easy-to-melt fibers and by heat treating, the short-cutstaple fibers were fused with each other and the short-cut staple fibersand the stereo-specific fibers of the supporting sheet were fused intheir contact points, so that stereo-specific networks were generated,which networks held the swollen SAP.

{circle around (2)} Dispersion of Absorbed Liquid

Although it was feared that the combination of the easy-to-meltshort-cut staple fibers and the thermal fusion of fibers by heattreatment would affect unfavorably the absorption and the diffusionspeed of a liquid, there was none or little influence on the absorbingtime and only a little influence on the time until diffusion wasfinished, which was a level never giving rise to any problems inpractical use at all.

Example 6

1) Preparing the SAP Slurries

To a 0.5% water dispersion liquid of the BC (made by Ajinomoto Co., Ltd.under the trade-mark “Bacteria Cellulose”) as the HFFM, required amountsof water and ethanol were added to prepare an ethanol/water dispersionliquid (the ratio of ethanol to water being 60 to 40) where theconcentration of the BC is 0.21% by weight.

To this dispersion liquid, PE pulp (made by Mitsui Chemical Co., Ltd.under the trademark “SWP-E400”) of 0.1 to 3 denier and 0.3 to 5 mm fiberlength as the short-cut staple fiber component was added in amounts tomake seven ratios of the short-cut staple fiber component to BC (P/Qratio), and the mixture was dispersed uniformly by a mixer to prepareseven kinds of dispersion liquid of different mixing ratios.

In addition, to each of the seven kinds (different in mixing ratios ofthe BC and the SWP) of BC/SWP dispersion liquid while it was stirred bya propeller mixer, a required amount of the SAP (made by MitsubishiChemical Co., Ltd. under trademark “Aquapearl”) was added to prepareseven kinds of three component slurry. In all the three-componentslurries the concentration of the SAP was 15% and the ratio of the BC tothe SAP was 1%. The concentrations of the components and the dispersionof the SAP in all the three component slurries are shown in Table 10below:

TABLE 10 Concentration 0.15 0.15 0.15 0.15 0.15 0.15 0.15 of BC (P) (%)Concentration 0.015 0.03 0.05 0.15 0.45 0.75 1.50 of SWP (Q) (%) P/Qratio 10/1 5/1 3/1 1/1 1/3 1/5 1/10 Suspension SWP SWP SWP SWP SWP notSWP SWP of stably stably stably stably coagurated, coagurated,coagurated SWP though but can be like soybean concentration used ascake, and can gets high. slurry. not be used as slurry.

In the P/Q ratios of 10/1 to 1/3 (concentration of the SWP being 0.45%),there was no coagulation of the SWP and the SWP was stably dispersed,but when the ratio exceeded 1/5 (concentration of the SWP being 0.75%),the slurry became cloudy with a little coagulation seen but still couldbe practically used. However, in case the P/Q ratio was around 1/10, theSWP coagulated too much to make a slurry. Therefore, from the viewpointof stable dispersion, the upper limit was judged to be 1/5 for practicalpurposes.

2) Preparing Supporting Sheets

A two-layered through-air thermal bond non-woven fabric was prepared,with a first layer composed of a mixed carded web of 50% rayon of 1.5denier and 40 mm length and 50% PE/PET bicomponent fiber of 2 denier and51 mm length and a second layer composed of only PE/PET bicomponentfiber of 3 denier and 51 mm length laid on each other and bonded in hotair. The weight of the non-woven fabric was 30 g/m², and the apparentspecific density was 0.02 g/cm².

3) Preparing Composite Absorbent

Onto the second layer of this supporting sheet each of the six kinds ofthree-component slurry (excepting the one which could not be preparedinto a dispersion slurry because of the P/Q ratio 1/10 from the sevenkinds of the three-component slurry) was applied by a coater in anamount to make the deposited amount of the SAP 150 g/m². After suckingand removing the liquid component were done, supporting sheets were heatpressed for several minutes by means of a heated roller at 180° C. andthen dried in hot air to prepare six kinds of composite absorbent (III)to (VIII).

<Evaluating Composite Absorbents>

For the six kinds of composite absorbent the sustainability of theswollen SAP and the diffusion of absorbed liquid by the swollen SAP whenwet were tested by the above-described testing methods. The test resultsare summarized in the following table:

TABLE 11 Sustainability of swollen SAP Dispersion of absorbed liquidComposite P/Q Standing Standing Vertically Absorbing Time tilldispersion absorbent ratio sustainability sustainability suspended time(sec.) finished (sec.) (III) 10/1 ○ ○ ○  3~5  50~60 (IV)  5/1 ⊚ ○ ○  5~7 50~60 (V)  3/1 ⊚ ○ ○  6~8  60~80 (VI)  1/1 ⊚ ⊚ ⊚  8~10  80~100 (VII) 1/3 ⊚ ⊚ ⊚ 20~30 150~200 (VIII)  1/5 ⊚ ⊚ ⊚ 30~50 240~300

From the above-tabulated test results the following judgements can bemade:

{circle around (1)} Sustainability of the Swollen SAP

In the composite absorbent where the content of the SWP was low(P/Q=10/1), no remarkable improvement in sustainability of the swollenSAP was seen, but as the content of the SWP increased, thesustainability of the swollen SAP improved: at around 3/1 of the P/Qratio, the retention reached a nearly constant level, and at the P/Qratio of 1/1 or higher, the sustainability of the swollen SAP in wetstate was excellent. The lowest limit for realizing the effects of theSWP seemed to be around the P/Q ratio of 5/1 for practical purposes.

{circle around (2)} Dispersion of Absorbed Liquid

The speed of a composite absorbent absorbing a liquid and the speed ofthe absorbed liquid being dispersed in the composite absorbent wereaffected by the concentration of a short-cut staple fiber componentcombined and the P/Q ratio. For example, in the absorbent composites(III) to (VI) of the P/Q ratio ranging from 10/1 to 1/1, there was noappreciable difference among them and they were all good: However, inthe absorbent composites (VII) and (VIII) of the P/Q ratio of 1/3 and1/5, while the sustainability of the swollen SAP improved, theabsorption of a liquid and the diffusion of a liquid tended to belowered.

Example 7

1) Preparing a SAP Slurry

To a 2.15% water dispersion liquid of the S-MFC (made by Tokushu PaperMfg. Co., Ltd. under the trademark “Super Micro Fibril Cellulose”),required amounts of water and propylene glycol were added to prepare awater/propylene glycol (PG) dispersion liquid (PG/water=70/30) where theconcentration of the MFC was 0.86% by weight. To this dispersion liquid,a required amount of the SAP (made by Mitsubishi Chemical Co., Ltd.under the trademark “Aquapearl US-40”) was added to prepare atwo-component slurry of 30% by weight SAP and 0.6% by weight MFC.

2) Preparing a Supporting Sheet

A two-layered through-air thermal bond non-woven fabric was prepared,with a first layer composed of carded web of PE/PET bicomponent fibersof 1.5 denier and 51 mm length and a second layer composed of PE/PETbicomponent fibers of 3 denier and 51 mm length laid on each other andbonded in hot air. The weight of this non-woven fabric was 30 g/m², andthe apparent specific density was 0.03 g/cm³.

3) Preparing a Composite Absorbent

The supporting sheet was placed on a plastic net with the second layerfacing upward, and the above-described two-component slurry was appliedby a roll coater onto the whole surface of the supporting sheet, as itwas continuously conveyed, in an amount to make the deposited amount ofthe SAP 200 g/m². Immediately thereafter, sucking and removal of theliquid component were carried out. Then, a 0.5% wood pulp dispersionliquid was poured onto the slurry layer as a thin layer stream from aflow coater in an amount to make the wood pulp 2% (4 g/m²) to the SAP.Immediately thereafter, sucking and removal of the liquid component wererun so that no SAP swelled, the supporting sheet was then hot pressedfor several minutes by means of a heated roller whose surfacetemperature was 150° C. Further, the supporting sheet was again dried inhot air at 140° C. to make a composite absorbent.

<Evaluating the Composite Absorbent>

The composite absorbent showed an outstanding sustainability of theswollen SAP: No swollen SAP came off or peeled off from the substrate.Also, since the surface of the supporting sheet was coated withhydrophilic wood pulp, the absorbency of a liquid was excellent and thediffusion of an absorbed liquid was also at a level not giving rise toany practical problems. It was confirmed that, when this compositeabsorbent was used as the absorbent of a baby diaper, no additionalnon-woven fabric layer for acquisition was required because, as thefirst layer and the topsheet were used as bonded together, the firstlayer functioned as the acquisition layer.

Example 8

The surface of a wet process non-woven fabric of 40 g/m² weight (made byFutamura Chemical Industries Co., Ltd. under the trademark “TCF 404”)was raised by a brush to make the apparent specific density 0.04 g/cm³.

On the raised surface of this supporting sheet, the SAP particles (madeby Mitsubishi Chemical Co., Ltd. under the trademark “US-40”) wasscattered using a sieve as it was vibrated in an amount to make thescattered amount of 120 g/m².

Separately, a mixture dispersion liquid where the S-MFC andeasy-to-dissolve-in-hot-water PVA staple fiber (of 1.5 denier and 2 mmlength) were dispersed in water in a way that the concentration of eachof the MFC and the PVA fiber was 0.5% was prepared. The raised surfaceof the supporting sheet was coated with the mixture dispersion liquid bya flow coater in an amount to make the percentage each of the S-MFC andthe PVA fiber to the SAP 1% (1.5 g/m²), and immediately thereafter,sucking and liquid removing of the liquid component were run. Then, thesupporting sheet was hot pressed by a roller heated at 200° C., anddried in hot air at 100° C. to make a composite absorbent.

Only a little SAP came off or peeled off from the obtained compositeabsorbent, and thus had a level of sustainability of the swollen SAP notgiving rise to any practical problems. The absorbing and diffusion of aliquid were extremely good. This was probably because both thesupporting sheet and the short-cut staple fiber component werehydrophilic.

Example 9

1) Preparing a Three-Component Dispersion Liquid

1.4 denier and 3 mm length Lyocell (trademark, made by Coutaulds) wasadded to and dispersed in a dispersion medium of ethanol/water=60/40 toprepare a 0.5% dispersion liquid. This dispersion liquid was stirred bya mixer to fibrillate Lyocell. Then, the MFC was added to and dispersedin the dispersion liquid in an amount to make the concentration of theMFC in the dispersion liquid 0.5%, and the dispersion liquid was treatedfor 5 minutes by a mixer to prepare a two-component dispersion liquid.

SAP flake (made by Hoechst-Celanese under the trademark “IM-4000”) of 50mesh was added to the two-component dispersion liquid while thedispersion liquid was slowly stirred in an amount to make theconcentration of the SAP 25%, to make a three-component dispersionliquid of the SAP, the MFC and Lyocell.

2) Preparing a Supporting Sheet

A mixed carded web was prepared composed of 50% rayon staple fiber (of1.5 denier×35 mm length) and 50% PE/PET bicomponent fiber (of 3denier×41 mm length) with the weight of 15 g/m², and the carded web laidon PP spun-bond non-woven fabric of 15 g/m² weight was entangled bywater jet to make a plural layered non-woven fabric, which was made asupporting sheet.

3) Making a Composite Absorbent

As shown in FIG. 81, the three-component slurry 822 was discharged froma plurality of discharging tubes directly connected to a slurry pumponto the rayon staple fiber/bicomponent fiber surface of a supportingsheet 821 in the pattern as shown in FIG. 81. After removal of theliquid component under reduced pressure, the supporting sheet was fixedby a heat press and dried to make a composite absorbent.

The obtained composite absorbent was approximately 130 g/m² in terms ofthe total SAP applied, and the portions (SAP) formed in lines on theobtained composite absorbent was approximately 200 to 250 g/m².

4) Applying to the Absorbent for Use in Baby Diaper

As shown in FIG. 82( a), a dry laid carded web non-woven fabric 831 asthe topsheet in contact with the skin of a wearer, as mainly composed of18 g/m² PE/PET bicomponent fiber of 1.5 denier×41 mm length wasprepared. Onto this non-woven fabric 831, polyurethane filament yarns832 (made by Toray Co., Ltd. under the trademark “Lycra”) was bonded byhot melt method in rows at such intervals as shown in FIG. 82( a) toform a topsheet. The topsheet provided with an elastic member and acomposite absorbent 833 as shown in FIG. 82( b) obtained in this Example9 of the present invention were bonded by thermal fusion at the portionswhere no absorbent existed thereby a bonded member of the topsheet andthe composite absorbent having a structure shown in FIG. 82( c) wasobtained.

The bonded member was covered at the side of the composite absorbent bya leakage resistant member 834 made by bonding PE film and non-wovenfabric as shown in FIG. 82( d) to obtain an absorbent for use in a babydiaper, of 200 mm width and 400 mm length. This absorbent was dipped ina physiological saline solution and then taken out and placed on a netso that a free liquid is removed from the absorbent. The total amount ofthe solution absorbed, as measured, was 600 cc. The initial penetrationspeed was 20 seconds with 100 cc, and the rewet was 0.5 gram. Thus, thecomposite absorbent of the present invention was proved to haveexcellent properties as the absorbent.

5) Applying for Use in Incontinent Pad for Women

As shown in FIG. 83, a slurry of the above-described composition 842 wasapplied onto a circular supporting sheet 841 as shown in FIG. 83( a) ina doughnut shape of 120 mm a circular supporting sheet 841 as shown inFIG. 83( a) in a doughnut shape of 120 mm diameter with a center hole of50 mm diameter, and, after drying, the surface was covered with ahydrophobic spun-bond 843 to make a composite absorbent. This compositeabsorbent was folded in a folding fan-like shape as shown in FIG. 83(c), and the tip of the composite absorbent was covered with an aperturedPE non-woven fabric 844 to make an incontinent pad of a structure asshown in FIG. 83( d). No absorbent existed at the portion where theapertured PE non-woven fabric 844 was provided and the portion which wasin thin sheet was for partial insertion in a vagina for securing the padto the body of a wearer. The amount of liquid retained by thisincontinent pad was 50 cc, and the incontinent pad was used as a samplein a wearing test by a patient having a light incontinence with theresult that the patient's underwear was not stained and that it can beused stably.

Example 10

Preparing a Slurry

A water dispersion stock solution of 3% by weight S-MFC was added tomake a dispersion medium composed of 60 parts ethanol and 40 partswater, to prepare a dispersion liquid of 0.6% by weight S-MFC. Into thisdispersion liquid, the SAP equivalent to 30% by weight (made byMitsubishi Chemical Co., Ltd. Under the trademark “US-40” with theaverage particle diameter of 200 microns) was added while the SAP wasstirred by a propeller mixer to prepare a slurry.

<Forming with the Slurry Pattern on a Supporting Sheet>

Using a slurry coating apparatus as shown in FIG. 76 (a slurrydischarging part thereof being shown, as enlarged, in FIG. 66), theslurry was applied onto the top surface of 40 g/m² TCF (cellulosicnon-woven fabric) used as a supporting sheet to form a pattern of slurryby means of tube pumps arranged in many rows in an amount to make theaverage deposited amount of the SAP 125 g/m². By the pulsation generatedby the stroke of the tube pump, a sheet having the ellipsoidal patternwhich has intermittently thicker slurry in the center regions wasformed.

<Bonding the Slurry Formed in a Pattern to the Supporting Sheet>

A supporting sheet on which the slurry was formed in, a pattern was hotpressed by means of a hot press roll of 160° C. and a suction roll, asshown in FIG. 76, and at the same time an excess of the dispersionmedium was sucked and removed. Thereafter, the sheet was made to contactwith a hot roll for approximately 5 seconds to remove the liquidcomponent from the sheet and the applied slurry was bonded to thesupporting sheet securely. Afterwards, the supporting sheet was peeledoff from the hot roll and air dried to make an absorbent sheet. At thattime, there was no deposit of the slurry on the hot roll becausepartially peeled off from the supporting sheet. For comparison, thesheet was passed at room temperature, with the hot roll not heated, inwhich case a majority of the slurry formed in a pattern on thesupporting sheet was peeled off and deposited on the surface of theroll. From this fact the effects of bonding the SAP to the supportingsheet by hot roll were be confirmed.

After hot pressing, the dried sheet showed a distribution of patterns asshown in FIG. 55. The bonding to the supporting sheet was as shown in afragmentary sectional view of FIG. 56, and the applied SAP was in onelayer at the thin regions, in nearly three layers at the thick regionsand in nearly two layers at the medium regions. This difference inthickness, or in the number of layers, gave a desired distribution ofthe concentrations which were not uniform, but continuous.

<Properties of Pattern-Formed Sheets>

A sample piece taken from each of the regions having the thick SAPpattern, the thin SAP pattern and the medium SAP pattern was observed incross-section by a magnifying glass, to confirm the number of the SAPlayers whereby the amount of absorbed liquid and the absorbing speedwere evaluated as the liquid absorbing properties of the SAP.

{circle around (1)} Amount of absorbed liquid: Using a 0.9% NaCl aqueoussolution (physiological saline solution), a method corresponding to amethod of testing an amount of absorbed water of JIS K-7223 was applied.

{circle around (2)} Absorbing speed: A plurality of sample pieces ofapproximately 5 mm×10 mm were dipped in a large amount of a 0.9% NaClaqueous solution and the time until the SAP in a sample became nearlycompletely swollen in seconds was measured.

For the amount of liquid absorbed, sample pieces of 10 cm×10 cm weretaken from the supporting sheet including from thickly to thinly coatedportions and as the average value of the whole sheet, the total amountof liquid absorbed was 6.0 kg/m². As the process of absorbing a liquidwas observed, it was confirmed that the thinly coated region, first,absorbed, and the absorbing progressed gradually to the medium coatedand then to the thickly coated region. The differences in liquidabsorbing speed among the regions are shown in Table 12:

TABLE 12 Thinly coated Medium coated Thickly coated Region of region(one region (two region (three sample layer of SAP) layer of SAP) layerof SAP) Absorbing 10-15 30-60 90-180 speed (sec.)

From the above-tabulated results, it was confirmed that the obtainedabsorbent sheet was flexible and had a characteristic property ofproviding a distribution of highly absorbing regions different inabsorbing speeds.

Example 11

<Preparing a Slurry from the Sap Having Different Particle Diameters>

The SAP whose average particle diameters were 200 microns and 800microns were prepared. As the 200 micron sample Mitsubishi Chemical'sUS-40 as used in Example 10 was used as the blank, while as the 800micron sample a pelletized SAP with higher surface cross-linking wasused.

The following table shows the measurements of the time of absorbing 20cc of physiological saline solution by 1 g of the SAP: As for the timeof absorbing a liquid by the SAP (Refer to Example 10 above), as theparticle diameter became larger, liquid took more time to penetrate intoinside and the swelling became lower.

TABLE 13 Average particle diameter of SAP (micron) 200 800 Speed ofabsorbing liquid 10-15 60-150

Two kinds of slurry of 30% by weight SAP having the above-describedproperties were prepared in the same way as in Example 10 above.

<Coating of a Supporting Sheet with the Slurry>

Two headers were provided on a slurry coating apparatus as shown in FIG.66 in order to feed two kinds of slurry containing the SAP whoseparticle diameters were different, and the apparatus was modified tofeed different kinds of slurry alternately to the respective pumps.

Using this apparatus, two kinds of slurry were deposited in a pattern onthe TCF side of a supporting sheet in an amount to make the averagedeposited amount of SAP 125 g/m², respectively, in a procedure similarto the one applied in Example 10 above. Thus, absorbent sheets with theslurry deposited in a pattern were obtained. In the distribution of thepattern in this case, as mentioned in the above, the rows of the patternwere coated with the SAP of different particle diameters alternately.Although the SAP of the same concentration was applied, because of thedifference in particle diameter, the pattern where larger particlediameter SAP was applied was relatively thick.

The obtained sheet on which the SAP of different particle diameters wasapplied was cut into a size of 10 cm×10 cm, and placed in a Petri dish.60 cc of physiological saline solution was added at three times of 200cc each at 5 minute interval, and the state of absorption was observed.The observation results are shown in Table 14.

It was confirmed that finer particle SAP first swelled and theabsorption progressed to coarser particle diameters.

TABLE 14 Patterns in absorbent layer Patterns in absorbent layer Liquidcomposed of SAP of small composed of SAP of large supplied particlediameter particle diameter First 200 cc Swelling rapidly started Surfacea little seemed to be absorbing, but nearly dry condition continuedSecond 200 cc Swelling reach saturation Overall swelling started, butthere remained ample room left for absorbing Third 200 cc Excess ofwater travelling in Swollen overall and reaching supporting sheet andsaturation transferred to patterns of larger particle diameter SAP

Example 12

<Preparing a First Dispersion Liquid>

To wood pulp (made by Weyerhaeuser, NBKP, needle leaf wood bleachedkraft pulp) and the SAP (made by Hoechst-Celanese under the trademark“IM-4500”), a small amount of thickener (P.E.O.) for paper-making wasadded to prepare a dispersion liquid of EtOH/water=50/50 containingpulp/SAP=4 parts/6 parts. The concentration of thus prepared slurry wasapproximately 2%.

<Forming an Absorbent Sheet from the First Dispersion Liquid>

The above-described slurry dispersion liquid was poured onto a PE/PETnon-woven fabric (made by Unitika Co., Ltd. under the trade name“Elves”) of 20 g/m² treated to be hydrophilic disposed on a plastic meshof 60 mesh to prepare a wet formed absorbent mat. By pressing and dryingthis absorbent mat, an absorbent sheet having 100 g/m² absorbent layerscomposed of pulp/SAP=4/6 was obtained.

<Preparing a Second Dispersion Liquid>

A slurry was prepared by including 30% SAP and 0.6% MFC in a dispersionliquid of EtOH/water=6/4 prepared in a procedure identical with the oneapplied in Example 10 above.

<Forming an Absorbent Sheet from the Second Dispersion Liquid>

Onto an absorbent sheet made from the above-described first dispersionliquid having uniform layers of pulp/SAP, slurry was fed in a seaisland-like pattern at 5 mm intervals, using an experimental use tubepump (marketed under the trademark “MASTER FLEX”) with the seconddispersion liquid contained in a silicone rubber tube of 3 mm insidediameter. Then, the absorbent sheet was hot pressed, using aTeflon-coated domestic use iron heated at 130° C. and then dried. Thelayers formed from the second dispersion liquid had the SAP ofapproximately 120 g/m² on average, although thicker at some places andthinner at others.

<Absorbent Sheet Having Highly Absorbing Regions in a Sea Island Patternand its Properties>

Thus obtained absorbent sheet had a distribution of nearly uniformabsorbent layers (containing the SAP of approximately 60 g/m²) derivedfrom the first dispersion liquid and of absorbent layers (containing SAPof approximately 120 g/m²) derived from the second dispersion liquidwhich latter absorbent layers were distributed in a pattern given tailspartly to the pattern shown in FIG. 16. Thus, an absorbent sheet havinga thick and thin two layered structure was obtained.

The absorbent sheet was cut in 10 cm×10 cm to make a sample. The samplewas placed in a Petri dish, and 0.9% physiological saline solution waspoured to run multi times of absorbing test. The absorbing test was runfour times at 5 minute intervals with 15 cc each. The test results areshown in Table 15.

TABLE 15 Amount of water added State of absorption Results ofobservation First 150 cc Only thin layers Dispersed all over firstlayer, added absorbed second layer remained dry Second 150 cc Absorptionpartly Whole first layer became wet, but added moved from first layersecond layer only partly wetted to second layer Third 150 cc Wholesecond layers Boundary between first and added started to swell secondlayers still distinct Fourth 150 cc Whole first and Second layer muchswollen to added second layers swollen have ridges

Example 13

<Preparing a SAP Slurry>

A slurry composed of the SAP and the MFC was prepared in a procedureidentical with the one applied in Example 10 above.

<Preparing a Liquid Pervious Supporting Sheet>

An air laid pulp sheet containing the SAP (made by Honshu Kinoclothunder the trademark “B-SAP”) whose weight was 85 g/m² was prepared. Inthis pulp sheet, the SAP of 20 g/m² was blended.

<Discharging the Slurry to Form a Pattern>

The above-described slurry from a slurry pump was discharged in apattern arranged in many rows of bands having indefinite circumferenceeach onto the above-described supporting sheet, as moving, from a nozzlehaving a cleavage-like discharging outlet as shown in FIG. 68. Then, thesupporting sheet was pressed under pressure by a hot roll whose surfacetemperature was 140° C. and air dried to make an absorbent sheet. In thedistribution of the patterns on this absorbent sheet, absorbent layerswere distributed in a pattern similar to the one in the sketch of FIG.17.

Example 14

The HFFM (made by Daicel Co., Ltd. under the trademark “Cellish KY100G”)in gel state was dispersed in a dispersed medium of MeOH/water=70/30 tomake a dispersion liquid of 0.6% concentration. In 1 liter of thisdispersion liquid, 400 g of the SAP (made by Mitsubishi Chemical Co.,Ltd. under the trademark “US40”) was added and stirred to prepare aco-dispersion slurry of the HFFM and the SAP.

This co-dispersion slurry was applied on either surface of a cellulosenon-woven fabric of 30 g/m² (made by Futamura Chemical Co., Ltd. underthe trademark “TCF#403”), and the non-woven fabric was subjected toremoval of the liquid component and dried to obtain an absorbent sheet.The thickness of this absorbent sheet was approximately 0.6 mm and thecontent of the SAP was 150 g/m².

The absorbent sheet was cut in 350 cm×250 cm. As shown in FIG. 84, thesheet was folded inside at the position 75 mm each from both sides withthe surface coated with the SAP facing inside to make an absorbent.Then, as shown in FIG. 85, the sheet was bonded to a liquid impervioussheet 902 at the folded sides via adhesive 901 to make an absorbent tube900. The thickness of thus obtained absorbent tube 900 was 1.3 mmincluding the liquid impervious sheet 902.

Swelling test was run by pouring physiological saline solution of 200 cceach time twice, 400 cc in total, onto the absorbent side of theabsorbent tube. The result was that 2 minutes after the first 200 cc waspoured the absorbent side swelled in a tube having an ellipsoidalcross-section of approximately 6 mm thickness, and 2 minutes after thesecond 200 cc was poured, the thickness increased to approximately 12mm.

Example 15

A non-woven fabric (made by Oji Paper Co., Ltd. under the trademark“Teccel”) obtained by entangling PP/PE bicomponent spun-bond non-wovenfabric and pulp together in high pressure jet stream was prepared.

On the other hand, commercially available bio-cellulose gel wasdispersed in a dispersion medium of EtOH/water=60/40 to prepare adispersion liquid of 0.3% concentration. In 1 liter of this dispersionliquid, 400 g of the SAP (made by Mitsubishi Chemical Co., Ltd. underthe trademark “US 40”) was added and stirred to prepare a co-dispersionslurry of the HFFM and the SAP.

Either surface of the above-described non-woven fabric was line-coatedwith this co-dispersion slurry in a plurality of bands of 7 mm width at5 mm intervals, and the non-woven fabric was subjected to removal of theliquid component and dried to obtain an absorbent sheet.

The absorbent sheet was cut in 350 mm×250 mm, and then, the cut sheetwas folded with the SAP applied surface facing inside in a flatcylindrical shape as shown in FIG. 86, and the folded portions of bothsides were bonded together via adhesive 903 to make an absorbent tube900. The thickness of thus obtained absorbent tube was approximately 2mm.

Swelling test was run by pouring physiological saline solution of 200 cceach twice, 400 cc in total, onto the absorbent tube. The result wasthat 2 minutes after the first 200 cc was poured, the absorbent tubeswelled in a tube shape having a ellipsoidal cross-section ofapproximately 10 mm, and 2 minutes after the second 200 cc was poured,the thickness increased to approximately 20 mm.

Example 16

APP spun-bond of 18 g/m² and a mixed carded fiber web of 30 g/m²composed of 60% PET staple fiber (3 denier×51 mm length) and 40% rayonstaple fiber (1.5 denier×35 mm length) were prepared. Such mixed cardedweb laid on such spun-bond non-woven fabric was entangled in highpressure water jet stream to prepare a composite non-woven fabric of astructure as shown in FIG. 37.

The composite non-woven fabric was coated with a co-dispersion slurry ofthe HFFM and the SAP used in Example 14 above, and subjected to removalof the liquid components and dried to obtain an absorbent sheet ofapproximately 2 mm thickness composed of three layers of the spun-bondnon-woven fabric, the carded web, and the SAP layer fixed by the HFFM,only on either surface of which absorbent sheet the SAP particles werecarried at the density of 150 g/cm².

This absorbent sheet was cut in bands of 350 mm width, and the cut sheetwas formed in tube with both longitudinal sides made to face each otherat approximately 30 mm interval.

Separately, from a disposable diaper (manufactured by Kao Corporationunder the trade name “Super Merries (L size)”), the inner sheet and theabsorbent core were taken out, and, instead in the region where suchsheet and core existed as shown in FIG. 38, the above-describedabsorbent tube in contact with the exposed outer sheet of the diaper waslinked to the liquid impervious sheet at both side ends via adhesive.

On thus obtained diaper, absorbing tests were conducted in a proceduregenerally practiced in this field. As the result of the tests, thefollowing results were obtained:

{circle around (1)} Amount of rewet (3 minute interval)

First rewet (100 cc): 0.5 g

Second rewet (100 cc): 0.8 g

Third rewet (100 cc): 2.0 g

{circle around (2)} Total absorbed amount (physiological salinesolution): 680 cc

Retained amount: 480 cc

Example 17

A PE/PET bicomponent non-woven fabric of 20 g/m² weight (made by UnitikaCo., Ltd. under the trademark “Elves”) was stretched and heat set asshown in FIG. 57 to prepare a easy-to-elongate non-woven fabric. Thisnon-woven fabric had the following properties:

Weight 31.2 g/m² Thickness 0.24 mm Density 0.132 g/cm³ Breakingelongation 35% (MD)/370% (CD) 100% elongation modulus in CR 83 g/5 cm.

The above-described easy-to-elongate non-woven fabric was coated with aco-dispersion slurry of the HFFM and the SAP in a procedure identicalwith the one applied in Example 14 above, and heated and pressed andsubjected to removal of the liquid component and dried to obtain anabsorbent sheet with the SAP particles carried in a density of 180 g/m²only on either surface. The absorbent sheet was folded in tube with thesurface carrying the SAP facing inside. Both side ends of the sheet weremade to face and bonded at the meeting portion of both side ends with athermal adhesive tape disposed on the outside to prepare an absorbenttube of approximately 30 mm outer diameter having nearly circularcross-section.

Thus obtained absorbent tube was placed in a plastic vat, and ionexchanged water was poured on the absorbent tube until the tube did notabsorb water any more, and allowed to stand for 10 minutes. As a result,the diameter of the absorbent tube increased to 66 mm, but no SAP wasobserved to leak from the outside of the non-woven fabric.

Example 18

An elastic net of 60 g/m² weight commercially available on the marketwas prepared as an absorbent sheet, where polyethylene monofilaments aslongitudinal filament members and SEBS monofilaments as lateral filamentmembers were crossed at right angle with each other and bonded at thepoints of intersection.

Separately, a carded parallel web of 25 g/m² composed of the followingfibers A and B was prepared:

A: bicomponent fiber of 2 denier×51 mm length, composed of a randompolymer of poly-propylene as the core and ethylene/propylene as thesheath.

B: Lyocell made by Coutaulds of 1.5 denier×35 mm length.

A carded parallel web A was laminated on one surface of theabove-described elastic net and another carded parallel web B waslaminated on the other surface of the net, and the net with the cardedparallel webs were entangled by water jet stream one time each on thetop and the bottom side of the laminated members under the pressure of50 kg/cm² from a nozzle having orifices of 0.13 mm diameter provided at0.6 mm interval. Further, water stream was jetted from the top under thepressure of 80 kg/cm² from a nozzle having orifices of 0.13 mm diameterprovided in one row at 5 mm interval. Then, the laminated members weredehydrated and dried to make an easy-to-stretch non-woven fabric withbonded portions in parallel lines formed longitudinally, of a structureas shown in FIGS. 59 and 60.

The properties of the non-woven fabric were as follows:

Weight 110.00 g/m² Thickness 1.22 mm Tensile strength in CD 1.50 kg/5 cmElongation in CR 270.00% Elongation modulus in CD  50% 150 g/5 cm100% 200 g/5 cm 150% 320 g/5 cm(Notes) The above-described properties were measured under the followingconditions:

Tensile strength: A sample piece of 5 cm width and 15 cm length (thecross direction of the non-woven fabric being the longitudinal directionof the sample) was held at the holding distance of 10 cm, and elongatedat the rate of 30 cm per minute by means of a constant rate stretchingtype tensile tester. The load value at breaking was taken as the tensilestrength.

Elongation modulus: A sample piece of 5 cm width and 15 cm length (thedirection of the non-woven fabric being the longitudinal direction ofthe sample) was held at the holding distance of 10 cm, and elongated150% at the rate of 30 can per minute by means of a constant ratestretching type tensile tester. From the stress-strain curve obtained atthat time, the stress each at 50%, 100% and 150% elongation was readout. The readings were taken as the elongation modulus.

Thickness: The thickness was measured by a thickness gauge (made byDaiei Kagaku Seiki Co., Ltd. under the trademark “THICKNESS GAUGE”)under a load of 3 g per 1 cm².

The Lyocell side of the above-described easy-to-stretch non-woven fabricwas coated with a co-dispersion slurry of the HFFM and the SAP in aprocedure identical with the one applied in Example 14 above. Thenon-woven fabric was subjected to removal of the liquid component anddried to obtain an absorbent sheet with the SAP particles carried in adensity of 125 g/m² only on one surface. Further, a crushed wood pulplayer of 150 g/m² was laid on the side of the absorbent sheet thatcarried the SAP particles, with such side facing inside the absorbentsheet was folded in a tube with the side ends facing each other at 30 mminterval and bonded to a separately prepared polyethylene outer sheet bymeans of hot melt type adhesive to obtain an absorbent tube bonded in anintegrated way to the outer sheet. The thickness of this absorbent tubewas approximately 4 mm.

The thus obtained absorbent tube was placed in a plastic vat, and fromthe top of the absorbent tube ion-exchanged water was poured until theabsorbent tube did not absorb water any more, and allowed to stand for10 minutes. As a result, the thickness of the absorbent tube increasedto 30 mm, but no SAP was observed to leak to the outside of thenon-woven fabric.

Example 19

<Preparing a Liquid Impervious Sheet Having Dents on the Surface>

Polyethylene film of 30 microns having taper-like openings, as shown inFIG. 39, all over the surface (made by Tredgar under the trademark“VISPORE X-6170”) was prepared.

<Preparing a Slurry of Absorbent Materials>

Separately, MFC gel (made by Daicel Co., Ltd. under the trademark“Celish KY-100G”) was dispersed in a dispersion medium ofethanol/water=70/30 to prepare 1 liter of dispersion liquid of 0.5% MFC.To this dispersion liquid, 200 g of the SAP particles (made byMitsubishi Chemical Co., Ltd. under the trademark “US40”) was added toprepare a co-dispersion slurry of the SAP and the MFC.

<Preparing an Absorbent Sheet>

The above-described polyethylene film having openings was, with thesurface having larger openings facing upward, was coated with theco-dispersion slurry of the SAP and the MFC as the polyethylene film wasfed and conveyed on a belt conveyor of plastic belt of 80 mesh providedwith a suction zone.

In the suction zone the co-dispersion slurry of the SAP and the MFC onthe polyethylene film having openings was subjected to removal of theliquid component through the openings to fill inside the openings withthe solid substance in the slurry. Then, the solid substance was driedby blowing hot air of 80° C. onto the solid substance.

The openings of the absorbent sheet had, as observed by a microscope, astructure as shown in FIG. 40.

<Evaluating the Permeability>

Permeability tests were conducted on the absorbent sheet by a Garrettype test method provided in JIS P117. The result was that the airpermeability of the absorbent sheet was 100 sec/100 cc.

<Measuring the Water Resistance>

10 sheets of commercially available tissue were placed under theabsorbent sheet, and a water column of physiological saline solutionmade by utilizing a glass tube of 20 mm diameter was built covering theopenings filled with highly absorbent material to measure the waterresistance pressure. At the portion which was filled with the highlyabsorbent material, the SAP was observed to mount due to its swelling,and although the water column was raised up to 800 mm H₂O, the liquiddid not leak out to wet the tissue.

Example 20

<Preparing a Substrate for Liquid Impervious Sheet Material>

Hot melt type adhesive was sprayed on the surface of a matte-finishedpolyethylene sheet of 25 microns composed of LLDPE, and a spun-lacenon-woven fabric having a high elasticity in the cross directioncomposed of PP staple fiber (1.5 denier×35 mm length) was laid on thesprayed surface of the polyethylene sheet and pressed together as heatedto be bonded to prepare a composite of the non-woven fabric and the filmhaving a structure as shown in FIG. 42A.

This composite was treated in a process shown in FIG. 42. First, thecomposite was made to pass on a grid roll (crest pitch 10 mm, width oftop 0.5 mm, and depth 2 mm) of stainless steel whose surface temperaturewas 100° C. to make linear grooves formed on the film (step B of FIG.42), and then laterally extended 1.5 times to obtain a composite of thenon-woven fiber and the film with the film portion and the non-wovenexposed in bands (step C of FIG. 42).

<Preparing a Slurry of Absorbent Material>

Ethanol and water were added to a water dispersion liquid of 5% BC gel(made by Ajinomoto Corporation under the trademark “Biocellulose”) toprepare one liter of 0.4% dispersion liquid of ethanol/water=60/40. Tothis dispersion liquid the SAP particles (made by Mitsubishi ChemicalCo., Ltd. under the trademark “US 40”) of 0.3 mm average particlediameter were added to prepare a co-dispersion slurry of the SAP and theBC.

<Preparing an Absorbent Sheet>

The non-woven fabric and film composite was coated with theabove-describe co-dispersion slurry in 200 g/m² weight and approximately10 mm width in a way that the non-woven fabric portion was covered (stepD of FIG. 42).

<Preparing an Absorbent Composite Having Dents>

The above-described absorbent sheet was formed in a corrugated shape bymeans of a grooved guide, and was laid on a PE/PET spun-bond of 20 g/m²(made by Unitika Co., Ltd. under the trademark “Elves”) treated to behydrophilic to make an absorbent with a topsheet (step E of FIG. 42).

<Evaluating the Air Permeability>

Air permeability tests (of a Garret type provided for in JIS P8117) wereconducted on the above-described absorbent sheet with the result thatthe air permeability was good, 80 sec/100 cc.

<Wearing Tests of Absorbent Products>

10 pieces of baby diaper were made by attaching a gather and a fasteningtape to the above-described absorbent sheet having dents, and wearingtests were conducted. With two pieces of baby diaper leakage occurredfrom the side portion, but no leakage occurred at all for the back sidewith any of the diapers.

Example 21

<Preparing a Water Resistant Material Having Dents and Projections>

An MS (melt-blown and spun-bond composite) non-woven fabric (18 g/m²)mainly composed of PP melt-blown (5 g/m²) and PP spun-bond (13 g/m²) wasprepared. On the other hand, an apertured film made by providingopenings of 2 mm diameter on PE film of 30 micron thickness mainlycomposed of LLDPE was prepared. A small amount of hot melt type adhesivewas sprayed onto the apertured film, and an MS non-woven fabric wasattached onto the sprayed side to obtain a composite sheet as shown inFIG. 43.

On this composite sheet a water column test was conducted in a procedureidentical with the one applied in Example 19 above with the result thatthe value was approximately 200 mm H₂O.

<Preparing an Absorbent Slurry>

An absorbent slurry was prepared under the same conditions as in Example19 above. The above-described composite of the MS non-woven fabric andthe apertured film was, in a procedure identical with the one applied inExample 19 above, supplied with the apertured film side facing upward ona conveyor belt provided with a suction zone and the absorbent slurrywas fed onto the composite. The composite was subjected to removal ofthe liquid component in the suction zone and the SAP particles asabsorbent material were bonded to and filled in the exposed surface ofthe MS non-woven fabric by means of the MFC to obtain an absorbent sheetas shown in FIG. 44.

<Air Permeability of the Absorbent Sheet>

Air permeability test (based on the Garret test provided for in JISP8117) was conducted on the obtained absorbent sheet with the resultthat the air permeability was 160 sec/100 cc.

<Evaluating the Water Resistance of the Absorbent Sheet>

10 sheets of tissue paper commercially available on the market wereplaced under the above-described absorbent sheet, a column ofphysiological saline solution was built by using a glass tube of 20 mmdiameter covering the openings which were filled with the SAP particlesto measure the water resistance. The SAP in contact with physiologicalsaline solution swelled to mount raising the water column up to 800 mmH₂O, but no liquid leaked nor the tissue wetted.

Example 22

<Varying Viscosity and Temperature of a Dispersion Slurry in a Processof Making a Composite>

FIG. 86 shows an example of a process of making a composite with the PGtaken as an example showing the varying viscosity and temperature of aslurry in each step of the process. In this example a dispersion slurrywas used where 30% SAP particles (made by Mitsubishi Chemical Co., Ltd.under the trademark “US 40”) and 0.5% MFC (made by Tokushu Paper Mfg.Co., Ltd. under the trademark “S-MFC”) were dispersed in a dispersionmedium of PG/water=70/30.

In preparing the dispersion slurry, stirring was required for mixing anddispersing the SAP and the MFC, and in order to save energy for stirringthe stirring was conducted at 30 t and 400 rpm. The obtained dispersionslurry was guided to a storage tank provided with a cooling jacket,where the slurry was stored at 10° C. while it was stirred slowly atapproximately 400 rpm, and from the storage tank was transferred to acoating header through a heating jacketed pipe by means of a Moino pump(made by Hyojin Pump Mfg. Co., Ltd.).

The coating header had a dwelling capacity of approximately 20 minutesand provided inside with a heating unit by a steam pipe. At this coatingheader, the temperature of the slurry was controlled at approximately50° C. The heated slurry was supplied to a coating roll provided with agrid, and applied in 10 mm width at 1 mm interval onto a non-wovenfabric. The non-woven fabric was Teccel of 50 g/m² (made by Oji PaperCo., Ltd.). The amount of coating was approximately 150 g/m². Thenon-woven fabric with the coated surface facing upward was guided tosteaming zones provided with a steam generator where adding of water andheating were performed, and then, was made to pass a reduced pressuresuction zone where the PG and water were removed. Remaining PG and waterwere further removed as the coated non-woven fabric was dried in hot airof 130° C. to make an absorbent sheet.

<Embodiments of the Present Invention in Dispersing Process>

The SAP particles/MFC were dispersed in a water/PG dispersion medium tomake a dispersion slurry. In a process of making a composite absorbentby forming the dispersion slurry, the SAP particles were bonded witheach other and the SAP and the substrate were bonded by the stronghydrogen bonds of the MFC covering the surface of the SAP particles.Hydrogen bonds were only completed with the PG removed first and thenmoisture removed, in a mixed dispersion medium system having highercontent of the PG. Also, since the boiling point of an aqueous solutionof the PG becomes lower, as the content of water becomes higher, it isadvantageous process-wise to have as much water as possible in theprocess for removing the PG.

TABLE 16 PG/water 90/10 80/20 70/30 60/40 50/50 Boiling point (° C.) 135116 110 106 104

On the other hand, however, as, in a dispersion medium of PG/water, thecontent of water was raised in the ratio of PG/water, the dispersionslurry containing the SAP became less stable as it changed against time,as shown in the following Table:

TABLE 17 Duration of stability of slurry PG/water containing SAPconfirmed Changing condition 80/20 Longer than 24 hours Not changed70/30 Around 4 hours Viscosity of system increased 60/40 Around 30minutes Viscosity of system rapidly increased 50/50 Around 5 minutesWhole solidified

It is, therefore, important from the technical viewpoint how to replacethe PG with water in the process. A first point of technical importanceis how a system where the content of water is high can be adopted, and asecond point of technical importance is how to replace the PG withwater, after the slurry system is formed into a sheet. FIG. 88 shows anembodiment of the present invention showing in which steps thepreparation of the dispersion slurry should be conducted leading to theslurry supplying zone of the forming process, i.e. the coating header.

Both of processes A and B are for preparing a dispersion slurry from adispersion medium of PG/water=70/30. In process A, a water dispersionliquid of the MFC is added to a SAP dispersion liquid of 100% PGeventually to make the ratio of 70/30. Suspending is a simple process,but stirring is important because in adding a water dispersion liquid ifthe water ratio is higher locally, the SAP swells and the dispersionsystem becomes non-uniform.

In process B, after a PG/water dispersion liquid of the MFC is preparedat the mixed ratio of 70/30, the SAP particles are dispersed. Thus, adispersion slurry can be prepared with relative ease.

In process C, when a slurry of mixed ratio of 70/30 obtained in the sameway as applied in process B is heated at a coating header, heating anduniformly adding of water are carried out at the same time in a shortperiod of time by adding steam directly, whereby the content of water isincreased in a short period of time, that is to say, only during thedwelling time at the header, and the viscosity is much lowered and theliquidity is increased by the heating and adding of water for formingthe coating.

In processes D and E embodying the present invention, an amount of wateris made relatively larger in a short period of the dwelling time of theslurry by making the addition of the SAP particles immediately beforethe header. In process D, a case is conceived that the amount of wateris made larger, i.e. the mixing ratio being 60/40, by adding the SAPparticles immediately before the header. Process E attempts to prepare adispersion slurry of higher water content, i.e. the mixing ratio being55/45, by preparing higher water content dispersion liquid of the MFCand adding to the dispersion liquid and mixing a 100% PG dispersionliquid of the SAP so that a uniform mixing is realized in a short periodof time immediately before the header.

<Embodiment of a Process of Removing the Liquid Component from PG/WaterDispersion Liquid System>

Embodiments of the present invention of preparing a dispersion slurry ofPG/water of higher water content were described in the above. In orderto efficiently remove the liquid component from a formed SAP sheetcontaining the PG and to have a higher content of water, such means areavailable as spraying water in droplets and making water stream flowingdown the sheet in thin layer by means of a flow coater so that the PG isreplaced with water. However, if such means is carelessly applied, thesurface of the sheet may be non-uniform.

FIG. 89 shows an example where steam is used in place of water stream asthe source for adding water and heating. This is an embodiment of thepresent invention showing a means for removing the liquid component inthe liquid phase by removing the liquid component under reduced pressurethe formed SAP sheet containing the PG and for afterwards removing theliquid component in the gas phase by hot press and hot air. A SAPcomposite sheet formed on a substrate from the PG/water medium in slurryof mixed ratio of 70/30 is guided together with the substrate to a firststeam treatment zone where heating and removing of the liquid componentunder reduced pressure are performed with the water content raised toapproximately 50/50 and the residual amount of the PG lowered, and thenguided to a second steam treatment zone. In the second steam treatmentzone, further heating and removing of the liquid component under reducedpressure with the water content raised to approximately 30/70 areperformed and part of the surface of the sheet is dried by hot presswith the content of the PG lowered so that the surface of the sheet isstabilized, and with the surface thus stabilized and with the content ofthe PG further lowered, the sheet is guided into a hot air dryer toremove water together with the PG so that eventually the liquid removedand dried highly absorbent sheet of the present invention may beobtained. It should be noted that in FIG. 89 the residual amount of thePG is indicated as a relative value when the residual amount of the PGin a sheet immediately after it is formed is 100.

The above-described examples are designed to provide a system of makinga highly absorbent sheet by utilizing a dispersion medium of apolyvalent alcohol and water as a dispersion medium of the SAP and bydexterously combining the viscosity and temperature characteristic ofthe dispersion medium in the configuration of the processes.

As described above, the absorbent composite of the present invention issuch that the water swollen solid member contained in the structure canbe formed in any shape such as powder, particle, pellet, sheet and anygiven three-dimensional structure and accordingly, the handling of theabsorbent composite is made easier and the range of its applications iswidened. When the SAP is utilized as such member and held stably in thenetwork structure of the HFFM, not only the SAP can be used as it is inparticles, but also an absorbent of any shape can be easily formed.Especially, formed in the shape of a sheet, the SAP can be made thinwhile having an extremely high capacity of absorbing water, and thethickness of absorbent products such as baby and adult diapers andfeminine hygiene products can be minimized to the limits.

In the present invention in case an absorbent layer of a compositeabsorbent provided at least on either surface of a supporting sheet iscomposed of three components consisting of the SAP particles, the HFFMand short-cut staple fibers, the SAP particles among themselves and thetop surface of layers formed by the SAP particles are covered in networkstructure by the short-cut staple fibers whose fiber length is longerthan the diameter length of the SAP particles so that the SAP is takenin the network structure whereby, even when swollen with liquid, theswollen SAP particles can be prevented from coming off.

Further, the absorbent sheet of the present invention, unlikeconventional absorbent sheets, can exhibit the capacity of absorbingquickly and stably many times body exudates discharged in varied waysand irregularly in terms of frequency depending upon environments andliving conditions, in addition to being of excellent flexibility.Besides, the absorbent sheet of the present invention very quicklyabsorbs a discharged liquid first time, but also similarly very quicklyabsorbs second and third times of repeated discharging.

In addition, in case a dispersion medium system composed of a polyvalentalcohol system or a polyvalent alcohol/water system, polyvalent alcoholbeing highly viscous at low temperatures and logarithmically reduced inviscosity as heated, is used, forming and removing of the liquidcomponent can easily be performed so that the efficiency of makinghighly absorbent sheets can be improved and the cost of making suchsheets can be reduced.

1. An absorbent sheet which comprises an absorbent layer consisting ofan absorbent composite comprising hydratable fine fibers in the form ofmicrofibril obtained from cellulose or a derivative thereof andabsorbent polymer particles, and a sheet supporting said absorbentlayer, wherein the ratio of said hydratable fine fibers in the form ofmicrofibril to said absorbent polymer particles is 0.3 to 20 percent byweight and said absorbent polymer particles are bonded together by saidhydratable fine fibers in the form of microfibril.
 2. The absorbentsheet of claim 1, wherein said absorbent composite is bonded on portionsof said supporting sheet, said portion forming a predetermined pattern.3. An absorbent sheet comprising a liquid pervious supporting sheet, andan absorbent layer consisting of an absorbent composite comprisinghydratable fine fibers in the form of microfibril and absorbent polymerparticles, wherein said absorbent layer is bonded on at least onesurface of said supporting sheet and forms a plurality of highlyabsorbing areas which have an absorbing capacity higher than theremaining areas and are distributed in a desired pattern on said liquidpervious supporting sheet and the ratio of said hydratable fine fibersin the form of microfibril to said absorbent polymer particles is 0.3 to20 percent by weight.
 4. The absorbent sheet of claim 3, which comprisessaid highly absorbing areas having said absorbent layer and the areas oflower absorbing capacity not having said absorbent layer.
 5. Theabsorbent sheet of claim 3, wherein the thickness of the absorbent layeris greater in the highly absorbent layer than in the remaining areas ofthe sheet.
 6. The absorbent sheet of claim 3, wherein said absorbentlayer in said highly absorbing areas becomes thinner toward areas oflower absorbing capacity adjoining to said highly absorbing areas. 7.The absorbent sheet of claim 3, wherein the density of said absorbentpolymer particles in said highly absorbing areas becomes lower towardareas of lower absorbing capacity adjoining to said highly absorbingareas.
 8. The absorbent sheet of claim 3, wherein said highly absorbingareas are bounded by peripheral lines.
 9. The absorbent sheet of claim3, wherein the pattern of said absorbent layer is in the shape of bandbounded by peripheral lines.
 10. The absorbent sheet of claim 3, whereinthe pattern of said absorbent layer on said liquid pervious supportingsheet is a gathering of mutually independent island areas.
 11. Theabsorbent sheet of claim 3, wherein the pattern of said absorbent layerconsists of a combination of rows of island areas and band areas havingvarying widths along the lengthwise direction.
 12. The absorbent sheetof claim 3, wherein said liquid pervious supporting sheet is ahydrophilic non-woven fabric.
 13. The absorbent sheet of claim 1,wherein said absorbent polymer particles are a combination of absorbentpolymer particles of plural kinds different in water absorbing capacityor shape.
 14. An absorbent sheet having a supporting sheet and anabsorbent layer provided on at least one surface of said supportingsheet, said absorbent layer comprising hydratable fine fibers in theform of microfibril, absorbent polymer particles, and a short-cut staplefiber component having a fiber length longer than the average diameterof said absorbent polymer particles, whereby said absorbent sheet has animproved dimensional stability when wet or swollen wherein the ratio ofsaid hydratable fine fibers in the form of microfibril to said absorbentpolymer particles is 0.3 to 20 percent by weight.
 15. The absorbentsheet of claim 1, wherein said absorbent layer contains 50 percent ormore of said absorbent polymer particles.
 16. The absorbent sheet ofclaim 1, wherein said supporting sheet is a porous non-woven fabrichaving an apparent density of 0.2 g/cm³ or lower.
 17. The absorbentsheet of claim 1, wherein said supporting sheet is a non-woven fabric,and at least part of said absorbent layer is entangled with saidnon-woven fabric.
 18. The absorbent sheet of claim 1, wherein a furthersheet material is bonded on said absorbent layer supported by saidsupporting sheet.
 19. The absorbent sheet of claim 1, wherein saidsupporting sheet comprises a first layer comprising cellulosic fiber anda second layer comprising synthetic fiber, wherein a density of saidcellulosic fiber is higher than-a density of said synthetic fiber. 20.The absorbent sheet of claim 14, wherein said short-cut staple fibercomponent does not swell substantially in response to water and has anaverage denier of 0.01 to 3.0.
 21. The absorbent sheet of claim 14,wherein said staple fiber component is a synthetic wood pulp comprisinga component with a melting point.
 22. The absorbent sheet of claim 14,wherein said short-cut staple fiber component is a composite fibercomprising a first component and a second component, wherein a meltingpoint of said first component is higher than a melting point of saidsecond component.
 23. The absorbent sheet of claim 14, wherein saidshort-cut staple fiber component comprises cellulose, and wherein saidsupporting sheet comprises a first layer consisting of a first compositefiber and a second layer consisting of a second composite fiber whereinsaid second composite fiber is coarser than said first composite fiberand said second layer is lower in density than said first layer.
 24. Theabsorbent sheet of claim 14, wherein the ratio of said hydratable finefibers in the form of microfibril (P) to said short-cut staple fibercomponent (Q) (P/Q) is in the range of from 1/5 to 5/1.
 25. Theabsorbent sheet of claim 1 which further comprises a short-cut staplefiber.
 26. The absorbent sheet of claim 25, wherein the short-cut staplefiber does not swell or dissolve in water and has an average denier ofabout 0.01 to about 3.0.
 27. The absorbent sheet of claim 26, whereinthe ratio of said hydratable fine fibers in the form of microfibril (P)to said short-cut staple fiber component (Q), (P/Q) is in the range offrom 1/5 to 5/1.
 28. The absorbent sheet of claim 27, wherein the ratioof said hydratable fine fibers in the form of microfibril (P) to saidshort-cut staple fiber component (Q), (P/Q) is in the range of from 1/3to 3/1.
 29. The absorbent sheet of claim 28, wherein said supportingsheet is a porous non-woven fabric having an apparent density of 0.2g/cm³ or lower.
 30. The absorbent sheet of claim 29, wherein theshort-cut staple fiber is a pulp state fiber.
 31. The absorbent sheet ofclaim 29, wherein the short-cut staple fiber is a short cut syntheticfiber.